Systems of zoological classification

Aristotle

Aristotle did not set out a classification of animals in tabular form, but from a study of his treatises Historia animalium[?], De generatione animalium[?], and De partibus animalium[?], the following classification can be arrived at:-

A. Evcsip.a, blood-holding animals (= Vertebrate).

I Z°~oro’.o~vra b’ etrouc, viviparous Enaema (= Mammals, ineluding the Whale).

2. OpsiO€i (=Birds).

3. Ttrpàirola ~ ~siroöa horosoipra, four-footed or legless Enaema which lay eggs (~Reptiles and Ainphibia).

4 ~Ix~’€c (~Fishes).

B. “Avai~ia, bloodless animals (= Invertebrata).

I. Ma?oh~ia, soft-bodied Anaema (= Cephalopoda).

2. MaXaK6urpa,ca, soft-shelled Anaema (= Crustacea).

3. Ei’rsua, insected Anaema or Insects (=Arthropoda, exclusive of Crustacea).

4. ‘OnrpaiwI~puera, shell-bearing Anaema (= Echini, Gasiropoda and Lamellibranchia).

Wotton follows Aristotle i in the division of animals into the Enaema and the Anaema, and in fact in the recognition of all the groups above given, adding only one large group Wotton’s to those recognized by Aristotle under the Anaema, modlikanamely, the group of Zoophyta, in which Wotton tions.

includes the Holotliurice, Star-Fishes, Medusae, Sea-Anemones and Sponges. Wotton divides the viviparous quadrupeds into the many-toed, double-hoofed and single-hoofed. By the introduction of a method of classification which was due to the superficial Pliny—depending, not on. structure, but on the medium inhabited by an animal, whether earth, air or water— Wotton is led to associate Fishes and Whales as aquatic animals. But this is only a momentary lapse, for he broadly distinguishes the two kinds.

The Swiss professor, Konrad Gesner (1516—1565), is the most voluminous and instructive of these earliest writers on systematic zoology, and was so highly esteemed that ~

his Historia animalium was republished a hundred es

years after his death. His great work appsared in successive parts—e.g. Vivipara, ovipara, ayes, pisces, Icr pentes et Scorpio

—and contains descriptions and illustrations of a large number of animal forms with reference to the lands inhabited by them. Gesner’s work, like that of John Johnstone (b. 1603), who was of Scottish descent and studied at St Andrews, and like that of Ulysses Aldrovandi of Bologna (b. 1522), was essentially a compilation, more or less critical, of all such records, pictures and relations concerning beasts, birds, reptiles, fishes and monsters as could be gathered together by one reading in the great libraries of Europe, travelling from city to city, and frequenting the company of those who either had themselves passed into distant lands or possessed the letters written and sometimes the specimens brought home by adventurous persons.

The exploration of parts of the New World next brought to hand descriptions and specimens of many novel forms of animal life, and in the latter part of the 16th century and the MedIC~1 beginning of the 17th that careful study by “special- anatomists “ of the structure and life-history of particular isis and groups of animals was commenced, which, directed microat first to common and familiar kinds, was gradually scop a. extended until it formed a sufficient body of knowledge to serve as an anatomical basis for classification. This minuter study had two origins, one in the researches of the medical anatomists, such as Fabricius (1537—1619), Severinus (1580—1656), Harvey (1578—1657), and Tyson (1649—1708), the other in the careful work of the entomologists and first microscopists, such as Malpighi (1628—1694), Swammerdam (I637—I68o), and Hook (1635—1702). The commencement of anatomical investigations deserves notice here as influencing the general accuracy and minuteness with which zoological work was prosecuted, but it was not until a late date that their full influence was brought to bear upon systematic zoology by Georges Cuvier

(1769—1832).

The most prominent name between that’ of Gesner and Linnaeus in the history of systematic zoology is that of John Ray (1628—1705). A chief merit of Ray is to have John

limited the term “species” and to have assigned to RaY.

it the significance which it bore till the Darwinian era, whereas previously it was loosely and vaguely applied. He also made

i If we remember that by “blood “ Aristotle understood “ red blood,” and that he did not know of the existence of colourless blood, his primary division is not a bad one. One can imagine the interest and astonishment with which the great Greek would have been filed had some unduly precocious disciple shown to him the red-blood-system of the marine terrestrial Annelids; the red blood of Planorbis, of Apus cancriformis, and of the Mediterranean razor shell, Solen legumen.

considerable use of anatomical characters in his definitions of larger gi~oups, and may thus be considered as the father of modern zoology. Associated with Ray in his work, and more especially occupied with the study of the Worms and Mollusca, was Martin Lister (1638—1712), celebrated niso as the author of the first geological map.

After Ray’s death the progress of anatomical knowledge, ‘md of the discovery and illustration of new forms of animal life From from distant lands, continued with increasing vigour. Ray to We note the names of Vallisnieri (1661—1730) and Lignaeus. Alexander Monro (1697—1767); the travellers Tournefort (I656—17o8) and Shaw (1692—1751); the collectors Rumphius (1637—1706) and Hans Sloane (1660—1753); the entomologist Réaumur (1683—1757); Lhwyd (1703) and Linck (1674—1734), the students of Star-Fishes; Peyssonel (b. 1694), the investigator of Polyps and the opponent of Marsigli and Réaumur, who held them to be plants; Woodward, the palaeontologist (1665—1722)—not to speak of others of less importance.

Two years after Ray’s death Carl Linnaeus (1707—1778) was born. Unlike Jacob Theodore Klein (I685--1759), whose careful Llnaaeus. treatises on various groups of plants and animals were

published during the period between Ray and Li.naeus, the latter had his career marked out for him in a university, that of Upsala, where he was first professor of medicine and subsequently of natural history. His lectures formed a new departure in the academic treatment of zoology and botany, which, in direct continuity from the middle ages, had hitherto been subjected to the traditions of the medical profession and regarded as mere branches of” materia medica.” Linnaeus taught zoology and botany as branches of knowledge to be studied for their own intrinsic interest. His great work, the Systeina natisrae, ran through twelve editions during his lifetime (1st ed. 1735, 12th 1768). Apart from his special discoveries in the anatomy of plants and animals, and his descriptions of new species, the great merit of Linnaeus was his introduction of a method of enumeration and classification which may be said to have created systematic zoology and botany in their present form, and establishes his name for ever as the great organizer, the man who recognized a great practical want in the use of language and supplied it. Linnaeus adopted Ray’s conception of species, but he made species a practical reality by insisting that every species shall have a double Latin name

—the first half to be the name of the genus common to several species, and the second half to be the specific name. Previously to Linnaeus long many-worded names had been used, sometimes with one additional adjective, sometimes with another, so that no true names were fixed and accepted. Linnaeus by his binomial system made it possible to write and speak with accuracy of any given species of plant or animal. He was, in fact, the Adam of zoological science. He proceeded further to introduce into his enumeration of animals and plants a series of groups, viz, genus, order, class, which he compared to the subdivisions of an army or the subdivisions of a territory, the greater containing several of the less, as follows:—

Class. Order. Genus. Species. Variety.

(,enus sum- Genus inter- Genus proxi- Species. Individuum.

mum. medium. mum.

Provincia. Territorium. Paroecia. Pagus. Domicilium.

Legio. Cohors. Manipulus. Contubernium. Miles.

Linnaeus himself recognized the purely subjective character of his larger groups; for him species were, however, objective:

“there are, “ he said, “just so many species as in the beginning the Infinite Being created.” It was reserved for a philosophic zoologist of the 19th century (Agassiz, Essay oil Classification, 1859) to maintain that genus, order and class were also objective facts capable of precise estimation and valuation. This climax was reached at the very moment when Darwin was publishing the Origin of Species (1859), by which universal opinion has been brought to the position that species, as well as genera, orders an’! clas’~es, are the subjective expressions of

a vast ramifying pedigree in which the only objective existences are individuals, the apparent species as well as higher groups being marked out, not by any distributive law, butby the interaction of living matter and its physical environment, causing the persistence of some forms and the destruction of vast series of ancestral intermediate kinds.

The classification of Linnaeus (from Syst. Nat., 12th ed., 1766) should be compared with that of Aristotle. ~

is as follows—the complete list of Linnaean genera cation of

being here reproduced:— Linnacus.

Class I. MAMMALIA.

Order f. Primates.

Genera: Homo, Simia, Lemur, Vespertilio.

2. Bruta.

Genera: Elephas, Trichecus, Brady pus, Myrmecophaga, Manis, Dasypus.

3. Ferae.

Genera: Phoca, Canis, Felis, Viverra, Mustela, Ursus, Dideiphys, Talpa, Sores, Erinaceus.

4. Glires.

Genera: Hystrix, Lepus, Castor, Mus, Sciurus,

Noctilio.

5. Pecora.

Genera: Ceemelus, Moschus, Cervus, Capra, Ovis,

Bos.

6. Belluae.

Genera: Equus, Hippopotamus, Sus, Rhinoceros.

7. Cete.

Genera: Monodon, Balaena, Physeter, Delphi nus.

Class II. Avas. -

Order i. Accipitres.

Genera: Vultur, Faico, Sins, Lanius.

“ 2. Picae.

Genera: (a) Trochitus, Certhia, 1/pupa, Buphaga,

Sitta, Or-iolus, Coracias, Gracula, Corvus, Para

disea; (b) Ramphastos, Trogon, Psittacus, Croto

phaga, Picus, Vans, Cuvulus, Bucco; (c) Buce

ros, Alcedo, Merops, Todos.

3. Anseres.

Genera: (a) Anas, Mergus, Phaeihon, Plotus;

(b) Rhyacops, Diomedea, Alca, Procellaria, Pelecanus, Larus, Sterna, Cot ymbus.

,, 4. Grallae.

Genera: (a) Phoenicopterus, Platalea, Palamedea, Mycteria, Tantalus, Ardea, Recurvirostra, Scolopaz, Tninga, Fule Ca, Parra, Rallus, Psophia, Cancroma; (b) Hemato pus, Charadrius, Otis, Strut hio.

5. Gallinae.

Genera: Didus, Pave, Meleagnis, Gras, Phasi anus, Tetrao, Numida.

,, 6. Passeres.

Genera (a) Loxia, Fringilla, Embeniza; (b)

Caprimulgus, Hirundo, Pipra; (c) Turdus,

Ampelis, Tanagra, Muscicapa; (d) Parus,

Motacilla, Alauda, Sturnus, Columba.

Class III. AMPI1IBIA.

Order I. Reptitia.

Genera: Testudo, Draco, Lacerta, Rena.

2. Sen pentes.

Genera: Crotalus, Boa, Coluber, Anguis, Amphisbaena, Caecilia.

3. lVantes.

Genera: Petromyzon, Raja, Squalus, Chimaera, Lophius, Acipensen, Cyctopterus, Balistes, Ostracion, Tetrodon, Diodon, Gentniscus, Syngnathus, Pegasus.

Class IV. PIscEs.

Order 1. Apodes.

Genera: Munaena, Gymnotus, Trichiurus, Anarrhichas, Ammodytes, Ophidium, Stromateus, Xiphias.

,, 2. Jugulares.

Genera: Callionymus, Uranosco pus, Trachinus, Gadus, Blennius.

3. Thoracici.

Genera: Ce pole, Echeneis, Cony phaena, Gobius, Coitus, Scorpaena, Zeus, Pleuronectes, Chaetodon, Sparus, Lebrus, Sciaena, Perca, Gasterosteus, Scomber, Mullus, Trigla.

4. Abdominales. -

Genera: Cobitis, Aniia, Silurus, Zeuthis, Lonfcaria, Salmo, F’istularia, Esox, Elops, Argentina, Atherina, Mugil, Mormyrus, Exocoetus, Polynemus, Clu’pea, C’vprinus.

Class V. INsEcTA.

Order 1. Coleoptera.

Genera: (a) Scarabaeus, Lucanus, Dermestes,

Hister, Byrrhus, Gyrinus, Attelabus, Curculio,

Silpha, Coccinella~ (b) Bruchus, Cassida, Plinus,

Chrysometa, His pa, Meioe, Tenebrio, Lam pyris,

Mo,della, Staphylinus; (c) Cerambyx, Leptura,

Cant hens, Elater, Cicindela, Bupreslis, Dytiscus,

Carabus, Necydalis, Forficula.

2. Hemi25tera.

Genera: Blatta, Mantis, Gryllus, - Fulgora, Cicada, Notonecla, Nepa, Cimex, Aphis, Chermes, Coccus, Thrips.

3. Lepidoptera.

Genera: Papilio, Sphinx, Phataena.

4. Neuroptera.

Genera: Libellula, Ephemera, Myrmeleon, Phryganea, Hemerobius, Panorpa, Raphidia.

5. Hymenoptera.

Genera: Cynips, Tent hredo, Sirex, Ichneumon, Sphex, Chrysis, Vespa, Apis, Formica, Mutilla.

6. Diptera.

Genera: Oeslrus, Tipula, Musca, Tabanus, Culex, Empis, Conops, Asilus, Bombyli-us, Hippobosca.

7. Aplera.

Genera: (a) Pedibus sex; capite a thorace discreto: Lepisma, Podura, Termes, Pediculus, Pulex.

(b) Pedibus 8—14; capite thoraceque unrtis:

Acarus, Phalangium, Aranea, Scorpio,

Cancer, Monoculus, Oniscus.

(c) Pedibus pluribus; capite a thorace discreto:

Scolopendra, Julus.

Class VI. VERMES.

Order 1. In/es/ma.

Genera: (a) Pertusa laterali poro: Lumbrzcus, Sipunculus, Fa5ciola.

(b) Imperforata poro laterali nub: Gordius, A scans, Hirudo, Myxine.

2. Mollusca.

Genera: (a) Ore supero; basi se afligens:

Actinia, Ascidia.

(b) Ore antico; corpore pertuso laterali foraminulo: Limax, Aplysia, Doris, Tethis.

(c) Ore antico; corpore tentaculis antice cincto: Holothuria, Terebella.

(d) Ore antico; corpore brachiato: Triton, Sepia, Clio, Lernaea, Scyllaea.

(e) Ore antico; corpore pedato: Aphrodita, Nereis.

Ci) Ore infero centrali: Medusa, Aslenia, Echinus.

3. Teslacea.

Genera: (a) Multivalvia: Chiton, Lepas, Pholas.

(b) Bivalvia (= Conchae): Mya, Solen, Tellina, Cardium, Mac/na, Donax, Venus, Spon-. dylus, Chama, Arca, Ostrea, Anomie, Mytilus, Pinna.

(c) Univalvia spira regulari (= Cochleae) : A rgonauta, - Nautilus, Conus, Cypraea, Bulla, Volula, Buccinum, Strombus, Murex, Trochus, Turbo, Helix, Nerita, Haliolis.

(d) Univalvia absque spira regulari: Pa/ella, Dentalium, Serpula, Teredo, Sabella.

4. Li/ho phyla.

Genera: Tubipora, Madre pore, Mille pore, Cellepora.

5. Zoophyta.

Genera: (a) Fixata: Isis, Gorgonia, Alcyonium, Spongia, Flustra, Tubular-ia, Corallina,

Sertularia, Vorticella.

(fi) Locomotiva: Hydra, Pennalula, Taenia, Volvox, Funia, Chaos.

The characters of the six classes are thus given by Linnaeus:— Cor biloculare, biauritum; ~ viviparis, Mammalibus;

Sanguine calido, rubro: ~ oviparis, Avibus.

Cur uniloculare, uniauritum; 1 ~ pulmone arbitrario, Amphibiis; Sanguine frigido; rubro: branchiis externis, Pisci bus.

Cor uniloculare, inauritum; ~ antennatis, Insectis;

Sanie frigida, albida: 1 tentaculatis, Vermibus.

1 The anatomical error in reference to the auricles of Reptiles and Batrachians on the part of Linnaeus is extremely interesting, since it shows to what an extent the most patent facts may escape the observation of even the greatest observers, and what an amount of repeated dissection and unprejudiced attention has been necessary before the structure of the commonest animals has become known.

Between. Linnaeus and Cuvier there are no very great names; but under the stimulus given by the admirable method and system of Linnaeus observation and description Prom of new forms from all parts of the world, both Linnaeus recent and fossil, accumulated. We can only cite the t~ Cuvier. names of Charles Bonnet (1720—1793), the entomologist, who described the reproduction of Aphis; Banks and Solander, who accompanied Captain Cook on his first voyage(1768 —1771); Thomas Pennant (1726—1798), the describer of the English fauna; Peter Simon Pallas (1741—1811), who specially extended the knowledge of the Linnaean Vermes, and under the patronage of the empress Catherine explored Russia and Siberia; De Geer (1720—1778), the entomologist; Lyonnet (17o7--1789), the author of the monograph of the anatomy of the caterpillar of Cossus ligniperdus; Cavolini (1756--I 810), the Neapolitan marine zoologist and forerunner of Della Chiaje (fi. 1828); 0. F. MUller (1730—1784), the describer of fresh-water Oligochaeta; Abraham Trembley (1700—1784), the student of Hydra; and 0. F. Ledermililer (1719—1769), the inventor of the term Infusoria. The effect of the Linnaean system upon the general conceptions of zoologists was no less marked than were its results in the way of stimulating the accumulation of accurately observed details. The notion of a scala naturac, which had since the days of classical antiquity been a part of the general philosophy of nature amongst those who occupied themselves with such conceptions, now took a more definite fos’m in the minds of skilled zoologists. The species of Linnaeus were supposed to represent a Series of steps in a scale of ascending complexity, and it was thought possible thus to arrange the animal kingdom in a single series—the orders within the classes succeeding one another in regular gradation, and the classes succeeding one another in a similar rectilinear progression.

J. B. P. de Lamarck (1744—1829) represents most completely, both by his development theory (to be further Lama,vk’s mentioned below) and by his scheme of classifica- classlfltion, the high-water mark of the popular but ~ fallacious conception of a scala naturae. His classification (1801—1812) is as follows:— Invertebrata.

1. Apathetic A-nimals.

Class I. INFUSORIA.

Orders: Nude, Appendiculata.

Class II. P0LYFI.

Orders: Cilia/i (Ro/ifera), Denude/i (Hydroids), Vagina/i (An/hozoa and Polyzoa), Na/an/es (Crinoids).

Class III. RADIARIA.

Orders: Mollia (Acalephae), Echinoderma (including Ac/iniae).

Class IV. TUNICATA.

Orders: Bothryllaria, A scidia.

Class V. VERMES.

Orders: Molles (Tape-Worms and Flukes), Rigiduli (Nematoids), Hispiduli (Nais, &c.), Epi~oaniae (Lernaeans, &c.).

2. Sensitive Animals.

Class VI. INSEcTA (Hexapoda).

Orders: A p/era, Diptera, Heiniptera, Lepidoptera, Hymeno p/era, Neuno p/era, Ortho p/era, Coleo p/era.

Class VII. ARACHNIDA.

Orders: A ntennato- Tracheal-ia’ (= Thysanura and Myniapoda), Exantennato- Trachealia, ExaijtennatoBranchialia.

Class VIII. CRU5TACEA.

Orders: Heterobranchia (Bnanchiopoda, Isopoda, Amphipoda, Stomapoda), Homobranchia (Decapoda).

Class IX. ANNELIDA.

Orders: Apoda, Antenna/a, Sedentania.

Class X. CIRRIPEDIA.

Orders: Sessilia, Pedunculata.

Class XI. CONCHIFERA.

Orders: Dim yania, Monomyania.

Class XII. MOLLUScA.

Orders: Pteropoda, Gasteropada, Trathelipoda, Cephalopoda, He/eropoda.

Vertebrata.

3. Intelligent Animals.

Class XIII. FIsHEs. Class XV~ BIRDS.

XIV. REPTILES. .. XVI. MAMMALS.

The enumeration of orders above given will enable the reader to form some conception of the progress of knowledge relating to the lower forms of life during the fifty odd years which intervened between Linnaetis and Lamarck. The number of genera recognized by Lamarck is more than ten times as great as that recorded by Linnaeus.

We have mentioned Lamarck before his great contemporary Cuvier because, in spite of his valuable philosophical doctrine of development, he was, as compared with Cuvier and estimated as a systematic zoologist, a mere enlargement and logical outcome of Linnaeus.

The distinctive merit of G. L. Cuvier (1769—1832) is that he started a new view as to the relationship of animals, which he Cuvier. may be said in a large measure to have demonstrated as true by his own anatomical researches. He

opposed the scala naturae theory, and recognized four distinct and divergent branches or embranc/iemens, as he called them, in each of which he arranged a certain number of the Linnaean classes, or similar classes. The embranchemens were characterized each by a different type of anatomical structure. Cuvier thus laid the foundation of that branching tree-like arrangement of the classes and orders of animals now recognized as being the necessary result of attempts to fepresent what is practically a genealogical tree or pedigree. Apart from this, Cuvier was a keen-sighted and enthusiastic anatomist of great skill and industry.~ It is astonishing how many good observers it requires to dissect and draw and record over and over again the structure of an animal before an appi ~ximately correct account of it is obtained. Cuvier dissected many Molluscs and other animals which had not previously been anatomized; of others he gave more correct accounts than had been given by earlier writers. Another special distinction of Cuvier is his remarkable work in comparing extinct with ‘recent organisms, his descriptions of the fossil Mammalia of the Paris basin, and his general application of the knowledge of recent animals to the reconstruction of extinct ones, as indicated by fragments only of their skeletons.

It was in 1812 that Cuvier communicated to the Academy of Sciences of Paris his views on the classification of animals. He says:— Si l’on considi~re le rbgne animal d’après les principes que nous

venons de poser, en Se debarassant des préjugCs établis sur les divisions anciennement admises, en n’ayant bgard qu’ a l’organisation et a Ia nature des animaux, et non pas a leur grandeur, a leur utilité, an plus ou moms de connaissance que nous en avons, ni a toutes les autres circonstances accessoires, on trouvera qu’il existe quatre formes principales, quatre plans gbnéraux, si l’on peut s’exprimer ainsi, d’après lesquels tous les anirnaux semblent avoir été rriodelbs et dont les divisions ultbrieures, de quelque titre oue les naturalistes les aient décorées, ne sont que des modifications assez lCgbres, fondées sur le dbveloppement, ou l’addition do quelques parties qui ne changent rien a l’essence du plan.”

Cuvi&s His classification as finally elaborated in Le Règne

~ Animal (Paris, 1829) is as follows:— First Branch. Anim’alia Vertebrata.

Class I. MAMMALIA. - - -

Orders: Biniana, Quadrumana, Carnivora, Marsu plaIf a, Rodentia, Edentala, Pachydermata, Ruminantia, Cetacea.

Class II. BIRDS. -

Orders: Accip-itres, Passeres, Scansores, Gallznae, Grallae, Palmipedes.

Class III. REI’TILIA.

Orders: Chelonia, Sauna, Ophidia, Bairachia.

Class IV. FISHES. -

Orders: (a) Acantlzopterygii, Abdominales, Subbrachii, A podes, Lophobranchii, Plectognathi; (b) Stuniones, Selachii, Cyclostomi.

Second Branch. Animalia Mollusca.

Class I. CEPHALOPODA.

Class IL PTEROPODA.

Class III. GASTROPODA.

Orders: Pulmonata, Nudibranchia, Inferobranchsa, Techbranchia, Heteropoda, Pect’inibranchia, Tubulibranchia, Scutibranchia, Cyclobranchia.

Class IV. ACE PHALA.

Orders: Testacea, Tunicata.

Class V. BRACHI0P0DA.

Class VI. CIRRIIOPODA.

Third Branch. Animalia Articulata.

Class I. ANNELIDES. - -

Orders: Tubicolae, Dorsibranchiae, Abranchzae.

Class II. CRUSTACEA.

Orders: (a)’ Malacostraca: Decapoda, Stomapoda, Amphipoda, Laemodipoda, Iso poda; (b) Entomostraca:

Branchiol,oda, Poecilopoda, Trilobitae.

Class III. ARAcHNIDES.

Orders: Pulmonaniae, Trachear’iae.

Class IV. INSECTS.

Orders: Jlzlyniapoda, Thysanura, Parasita, Suctoria, Coleoptera, Orihoptera, Ilemiptera, Neuroptena, ilymenoptena, Lepidoptera, Rhipiptera, Diptera.

Fourth Branch. Animalia Radiata,

Class I. EcisfNoDERMs.

Orders: Pedicellata, Apoda.

Class II. INTESTINAL WORMS.

Orders: Neaiatoidea, Parenchymatosa. Class III. ACALEPHAE.

Orders: Simplices, Hydrostaticae.

Class IV. POLYP1 (including the Coelentera of later authorities and the Polyzoa).

Orders: C’arnosi, Gelatinosi, Polypiari’i.

Class V. INFUSORIA.

Orders: Rotifera, Homogenea (this includes the Protozoa of recent writers and some Protophyla).

The leading idea of Cuvier, his four embranclzeme’ns, was confirmed by the Russo-German naturalist Von Baer (1792—1876), who adopted Cuvier’s divisions, speaking of them as Von Baer. the peripheric, the longitudinal, the massive, and the vertebrate types of structure. Von Baer, however, has another place in the history of zoology, being the first and most striking figure in the introduction of embryology into the consideration of the relations of animals to one another.

Cuvier may be regarded as the zoologist by whom anatomy was made the one important guide to the understanding of the relations of animals. But the belief, dating from Malpighi ~ (1670), that there is a relationship to be ‘discovered, hlo and not merely a haphazard congregation of varieties of structure to be classified, had previously gained ground. g Cuvier was familiar with the speculations of the “ Natur-philosophen,” and with the doctrine of transmutation and filiation by which they endeavoured to account for existing animal forms. The noble aim of F. W. J. Scheiling, “das ganze System der Naturlehre von dem Gesetze der Schwere his zu den Bildungstrieben der Organismus als em organisches Ganze dai’zustellen,” which has ultimately been realized through Darwin, was a general one among the scientific men of the year f8o0. Lamarck accepted the development theory fully, aiid pushed his speculations far beyond the realm of fact. The more cautious Cuvier adopted a view of the relationships of animals which, whilst denying genetic connexion as the explanation, recognized an essential identity of structure throughout whole groups of animals. This identity was held to be due to an ultimate law of nature or the Creator’s plan. The tracing out of this identity in diversity, whether regarded as evidence of blood-relationship or as a remarkable display of skill on the part of the Creator in varying the details whilst retainin the essential, became at this period a special pursuit, to whic Goethe, the poet, who himself contributed importantly to it, gave the name “ morphology.” C. F. Wolff, Goethe and Oken share the credit of having initiated these views, in regard especially to the structure of flowering plants and the Vertebrate skull. Cuvier’s doctrine of four plans of structure was essentially a morphological one, and so was the single-scale doctrine of Buffon and Lamarck, to which it was opposed. Cuvier’s morphological doctrine received its fullest development in the principle of the “ correlation of parts,” which he applied to palaeontelogical iavestigatlon, namely, that every animal is a definite whole, and that no part can be varied without entailing correlated and law-abiding varia~ tions in other parts, so that from’ a fragment it should be possible, had we a full knowledge of the laws of animal structure or morphology, to reconstruct the whole. Here Cuvier was imperfectly formulating, without recognizing the real physical basis of the phenomena, the results of the laws of heredity, which were subsequently investigated and brought to bear on the problems of animal strocture by Darwin.

Sir Richard Owen (1804—1892) may be regarded as the foremost of Cuvier’s disciples. Owen not only occupied himself with the dissection of rare animals, such as the Pearly Owen. Nautilus, Lingula, Limulus, Protopterus, Apteryx, &c., and with the description and reconstruction of extinct reptiles, birds and mammals—following the Cuvierian tradition—but gave precision and currency ,to the morphological doctrines which had taken their rise in the beginning of the century by

the introduction of two terms, “homology” and “analogy,” which were defined so as to express two different kinds of agreement in animal structures, which, owing to the want of such

counters of thought,” had been hitherto continually confused.

Analogous structures in any two animals compared were by O’ven defined as structures performing similar functions, but not necessarily derived from the modification of one and the same part in the “plan -‘ or “archetype” according to which the two animals compared were supposed to be constructed. Homologous ~tTuctures were such as, though greatly differing in appearance and detail from one another, and though performing widely different functions, yet were capable of being shown by adequate study of a series of intermediate forms to be derived from one and the same part or organ of the “ plan-form” or “archetype.” It is nut easy to exaggerate the service rendered by Owen to the study of zoology by the introduction of this apparently small piece of verbal mechanism; it takes place with the classificatory terms of Linnaeus. And, though the conceptions of “archetypal morphology,” to which it had reference, are now abandoned in favour of a genetic morphology, yet we should remember, in estimating the value of this and of other speculations which have given place to new views in the history of science, the words of the great reformer himself. “ Erroneous observations are in the highest degree injurious to the progress of science, since they often persist for a long time. But erroneous theories, when they are supported by facts, do little harm, since every one takes a healthy pleasure in proving their falsity “ (Darwin). Owen’s definition of analogous structures holds good at the present day. His homologous structures are now spoken of as “ homogenetic “ structures, the idea of community of representation in an archetype giving place to community of derivation from a single representative structure present in a common ancestor. Darwinian morphology has further rendered necessary thg introduction of the terms” homoplasy” and “homoplastic” (E. Ray Lankester, in Ann. and Mag. Nat. Hist. 1870) to express that close agreement in form which may be attained in the course of evolutional changes by organs or parts in two animals which have been subjected to similar moulding conditions of the environment, but have not a close genetic community of origin, to account for their similarity in form and structure, although they have a certain identity in primitive quality which is accountable for the agreement of their response to similar moulding conditions.

• The classification adopted by Owen. in his lectures (1855) Owen’s does not adequately illustrate the progress of zoological classifi- knowledge between Cuvier’s death and that date, but, cation, such as it is, it is worth citing here.

Province: Vertebrata (Myelencephala, Owen) -

Classes: MAMMALIA, AyES, REPTILIA, PISCES.

Province: Articulata.

Classes: ARACHNIDA, IN5ECTA (including Sub-Classes Myriapoda, Hexapoda), CRIJSTACEA (including Sub-Classes Entomostraca, Malacostraca), E PIZ0A (Epizootic Crustacea), ANNELLATA (Chaetopods and Leeches), CIRR1I-EDIA.

Province: Mollusca.

Classes: CEPHALOPODA, GASTEROPODA, PTEROPODA, LAMELLIISRANCHIATA, BRACHIOPODA, TUNICATA.

Province: Radiata.

Sub-Province: Radiaria.

Classes: ECHINODERMATA, BRYOZOA, ANTHOZOA, AcALEPHAE, HYDROZOA.

Sub-Province: Entozoa.

Classes: COELELMINTHA, STERELMINTHA.

Sub-Province; Infusoria.

Classes: ROT1FERA, POLYGASTRIA (the Protozoa of recent authors).

The real centre of progress of systematic zoology was no longer in France nor with the disciples of Cuvier in England, but after his death moved to Germany. The wave of morphological speculation, with its outcome of new systems and new theories of classification (see Agassiz, Essay on Classification, 1859), which were as numerous as the professors of zoological science, was necessarily succeeded in the true progress of the science by a period of minuter study in which the microscope, the discovery of embryological histories, and the all-important cell-theory came to swell the stream of exact knowledge.

The greatest of all investigators of animal structure in the 19th century was Johann Muller (1801—1858), the successor in Miller Germany of the anatomists Rathke (1793—1860)

and Meckel (1781—1833). His true greatness can only be estimated by a consideration of the fact that he was a great teacher not only of human and comparative anatomy and zoology but also of physiology, and that nearly all the most

distinguished German zoologists and physiologists of the period 1850 to 1870 were his pupils and acknowledged his leadership. The most striking feature about Johann Muller’s work, apart from the comprehensiveness of his point of view, in which he added to the anatomical and morphological ideas of Cuvier a consideration of physiology, embryology and microscopic structure, was the extraordinary accuracy, facility and completeness of his recorded observations. He could do more with a single specimen of a rare animal (e.g. in his memoir on Amphioxus, Berlin, 1844) in the way of making out its complete structure than the ablest of his contemporaries or successors could do with a plethora. His power of rapid and exhaustive observation and of accurate pictorial reproduction was phenomenal. His most important memoirs, besides that just mentioned, are those on the anatomy and classification 01 Fishes, on the Caecilians and on the developmental history of the Echinoderms.

A name which is apt to be forgotten in the period between Cuvier and Darwin, because its possessor occupied an isolated position in England and was not borne up by any j. v.

great school or university, is that of John Vaughan ThompThompson (1779—1847), an army surgeon, who in 1816 son.

became district medical inspector at Cork, and then took to the study of marine Invertebrata by the aid of the microscope. Thompson made three great discoveries, which seem to have fallen in his way in the most natural and simple manner, but must be regarded really as the outcome of extraordinary genius. He showed (1830) that the organisms like Flustra are not hydroid Polyps, but of a more complex structure resembling Molluscs, and he gave them the name Polyzoa He discovered (1823) the Pentacrinus europaeus, and showed that it was the larval form of the Feather-Star Antedosz (Comatula). He upset (5830) Cuvier’s retention of the Cirripedes among Mollusca, and his subsequent treatment ‘of them as an isolated class, by showing that they begin life as free-swimming Crustacea identical with the young forms of other Crustacea. Vaughan Thompson is a type of the marine zoologists, such as Dalyell, Michael Sars, P. J. Van Beneden, Claparède, and Ailman, who during the I9th century approached the study of the lower marine organisms in the same spirit as that in which Trembley and Schaffer in the 18th century, and Swammerdam in the 17th, gave themselves to the study of the minute fresh-water forms of animal life.

It is impossible to enumerate or to give due consideration to all the names in the army of anatomical and embryological students of the middle third of the I9th cen.tul’y whose labours bore fruit in the modification of zoological theories and in the building up of a true classification of animals. Their results are best summed up in the three schemes of classification which follow below—those of Rudolph Leuckart (1823—1896), Henri Milne-Edwards (1800—1884), and T. H. Huxley (1825—1895), all of whom individually contributed very greatly by their special discoveries and researches to the increase of exact knowledge.

Contemporaneous with these were various schemes of dassification which were based, not on a consideration of the entire structure of each animal, but on the variations of a Single.

single organ, or on the really non-significant fact of fact

the structure of the egg. All such single-fact systems s.vstems have proved to be departures from the true line of

growth of the zoological system which was shaping

itself year by year—unknown to those who so shaped it—as a genealogical tree. They were attempts to arrive at a true knowledge of the relationships of animals by “royal roads “; their followers were landed in barren wastes.

R, Leuckart’s classification (Die Morphologie un4 Leuckari’s die Verwandtschaftsverhaltnisse der wirbellosen Thiere, ~

Brunswick, 1848) 15 as follows:— Type I. Coelenterata.

Class I. POLYPI. -

Orders: Anlhozoa and Cylscozoa.

,, II. ACALEPIIAE. -

Orders: Disco phorae and Cteno~horae, -~

Type 2. Ecliinoderniata. -

Class I. PELMATOZOA. -

Orders: Cystidea and Crinoidea.

II. AcrINozoA.

Orders: Ecjijnjda and Asterida.

,, III. SCYTODERMATA.

Orders: Holothuriae and Sipunculida. Type 3. Vermes.

Class I. ANENTERAETI.

Orders: C’estodes and Acanthocephali.

II. APODES.

Orders: Nemertini, Turbellarii, Trematodes and H’irudinei.

,, III. CILIATI.

Orders: Bryozoa and Rot if era.

,, IV. ANNELIDES.

Orders: Nematodes Lumbricini and Branchiati.

Type 4. Arthropoda.

Class I. CRUSTACEA.

Orders: Enlomostraca and Malacostraca.

,, II. INSECTA.

Orders: Myriapoda, Arachnida (Acera, Latr.), and Hexapoda.

Type 5. Mollusca.

Class I. TUMCATA.

Orders: Ascid’iae and Salpae.

,, II. AcEPHALA.

Orders: Lamellibranchiata and Brachiopoda.

,,III. GASTEROPODA.

Orders: Heterobranchia, Dermatobranchia, Heteropoda, Ctenobranchia, Pulmonata, and Cyclo/jranchia.

IV. CEPI-JALOPODA.

Type 6. Vertebrata. (Not specially dealt with.)

Mime- The classification given by Henri Milne-Edwards

Edwards’s - . ,

classifi- (Cours Elemenlaire d Ilistoire Naturelle, Paris, 1855) callon. is as follows:— Branch I. Osteozoaria or Vertebrata.

Sub-Branch I. Allantoidians.

Class I. MAMMALIA.

Orders: (a) Monodelphia: Bimana, Quadrumana, Cheiroptera, Insectivore, Rodentia, Edenlate, Carnivora, Amphibia, Pachydermata, Ruminantia, Cetacea; (b) Didelphia: Marsup’ialia, Monotrernata.

,, II. BIRDS.

Orders: Rapaces, Passeres, Scansores, Gallinae, Grallae, Palmipedes.

,, III. REPTILES. -

Orders: çhelonia, Sauna, Ophidia. Sub-Branch 2. Anallantoidians.

Class I. BATRACHIANS.

Orders: Anura, Urodela, Perennibranchici, Caec~liae.

,, II. FIsi1Es.

Section 1. Ossei.

Orders: A canthopterygii, A bdominales, Subbrachii, A podes, Lophobranchii, Pleclognathi.

Section 2. Chondroplerygii.

Orders: Sturiones, Selachii, Cycloslomi.

Branch II. Entomozoa or Annelata.

Sub-Branch 1. Arthropoda.

Class 1. INSECTA.

Orders: Coleoptera, Onthoptera, Neuroplera, Hymenoptera, Lepidoptera, Hemiplera, Diplera, Rhipiptera, Anopleura, Thysanura.

‘ 11. MYRIAPODA.

Orders: Chilognatha and Chilopoda.

,, III. ARACHNIDS.

Orders: Pulmonania and Trachearia.

IV. CRUSTAcEA.

Section I. Podophthalmia.

Orders: Decapoda and Slomopoda. Section 2. Edniophthalmz.

Orders: A mphipoda, Loemodipoda and Isopoda.

Section 3. Branchiopoda.

Orders: Ostracoda, Phyllopoda and Trilobitae.

Section ~. Entemoslraca.

Orders: Copepoda, Cladocera, Siphonostoma, Lernaeida, Cirriped’ia.

Section 5. Xiphosura.

(The orders of the classes which follow are not given in the work quoted.)

Sub-Branch 2. Verines.

Class I. ANNELIDS. Class IV. CESTOIDEA.

,, II. HELMINTHS. ,, V. ROTATORIA.

,, III. TURBELLARIA.

Branch III. Malacozoaria or Mollusca.

Sub-Branch I. Mollusca proper.

Class I. CEPHALOPODA. Class III. GASTEROPODA.

,, II. PTEROPODA. ,, IV. ACEPHALA.

Sub-Branch 2. Mollsiscoidea,

Class I. TUNICATA. Class II. BgyozoA.

Branch IV. Zoophytes.

Sub-Branch I. Radiaria.

Class I. EcHINODERMS. Class III. CORALLARIA or

,, II. AcALEPHS. P0LYPI.

Sub-Branch 2. Sarcodaria.

Class I. INFUSORIA. Class II. SPONGIARIA.

In England T. H. Huxley adopted in his lectures huxley’s (1869) a classification which was in many respects ci&ssifisimilar to both of the foregoing, but embodied im- c8iiofl. provements of his own. It is as follows:— Sub-Kingdom I. Protozoa.

Classes: RHIZOr’oDA, GREGARINIDA, RADIOLARIA, SPONGIDA.

Sub-Kingdom II. Infusoria.

Sub-Kingdom III. Coelenterata.

Classes: HYDROZOA, AcTINozoA.

Sub-Kingdom IV. Annuloida.

Classes: SCOLECIDA, ECFIINODERMATA.

Sub-Kingdom V. Annulosa.

Classes: CRUSTACEA, ARACHNIDA,MYRIAPODA,INSECTA,CHAETOGNATHA, ANNELIDA.

Sub-Kingdom VI. Molluscoida.

Classes: POLYZOA, BRACHIOPODA, TUNIcATA.

Sub-Kingdom VII.’ Mollusca.

Classes: LAMELLIBRANCHIATA,B RANcHI0GASTR0POIYA,PULMOGASTROPODA, PTEROPODA, CEPHALOPODA.

Sub-Kingdom VIII. Vertebrata.

Classes: PISCES, AM1’HIBIA, REPTILIA, AYES, MAMMALIA.

We now arrive at the period when the doctrine of organic evolution was established by Darwin, and when naturalists, being convinced by him as they had not been by the transmutationists of fifty years’ earlier date, were compelled to take an entirely new view of the significance of all attempts at framing a “natural” classification.

Many zooi.ogists—prominent among them in Great Britain being Huxley—had been repelled by the airy fancies and assumptions of the “philosophical” morphologists. CiassifiThe efforts of the best minds in zoology bad been cist Ions directed for thirty years or more to ascertaining based on with increased accuracy and minuteness the struc- ~

ture, microscopic and gross, of all possible forms of lure.

animals, and not only of the adult structure but of the steps of development of that structure in the growth of each kind of organism from the egg to maturity. Putting aside fantastic theories, these observers endeavoured to give in their classifications a strictly objective representation of the facts of animal structure and of the structural relationships of animals to one another capable of demonstration. The groups within groups adopted for this purpose were necessarily wanting in symmetry: the whole system presented a strangely irregular character. From time to time efforts were made by those who believed that the Creator must have followed a symmetrical system in his production of animals to force one or other artificial, neatly balanced scheme of classification upon the zoological world. The last of these was that of Louis Agassiz (1807—1873), who, whilst surveying all previous ~ I classifications, propounded a scheme of his own

(Essay on Classification, 1859), in which, as well as in the criticisms he applies to other systems, the leading notion is that sub-kingdoms, classes, orders and families have a real existence, and that it is possible to ascertain and distinguish characters which are of class value, others which are only of ordinal value, and so on, so that the classes of one sub-kingdom should on paper, and in nature actually do, correspond in relative value to those of another sub-kingdom, and the orders of any one class similarly should be so taken as to be Of equal

value with those of another class, and have been actually so created.

The whole position was changed by the acquiescence, which became universal, in the doctrine of Darwin. That doctrine

took some few years to produce its effect, but it In/~uence became evident at once to those who accepted Darwinian winism that the natural classification of animals, dOc~fine after which collectors and anatomists, morphologists, ontaxo- philosophers and embryologists had been so long

Y~ striving, was nothing more nor less than a genealogical tree, with breaks and gaps of various extent in its record. The facts of the relationships of animals to one another, which had been treated as the outcome of an inscrutable law by most zoologists and glibly explained by the transcendental morphologists, were amongst the most powerful arguments in support of Darwin’s theory, since they, together with all other vital phenomena,’ received a sufficient explanation through it. It is to be noted that, whilst the zoological system took the form of a genealogical tree, with main stem and numerous diverging branches, the actual form of that tree, its limitation to a certain number of branches corresponding to a limited number of divergences in structure, came to be regarded as the necessary consequence of the operation of the physico-chemical laws of the universe, and it was recognized that the ultimate explanation of that limitation is to be found only in the constitution of matter itself.

The first naturalist to put into practical form the consequences of the new theory, in so far as it affected zoological

Ilaeckei classification, was Ernst Haeckel of Jena (b. 1834), who in 1866, seven years after the publication of

Darwin’s Origin of Species, published his suggestive Generelle 3lorphologie. Haeckel introduced into classification a number of terms intended to indicate the branchings of a genealogical tree. The whole “system” or scheme of classification was termed a genealogical tree (Stammbaum); the main branches were termed “ phyla,” their branchings “ sub-phyla “; the great branches of the sub-phyla were termed “cladi,” and the

cladi “ divided into “ classes,” these into sub-classes, these into legions, legions into orders, orders into sub-orders, suborders into tribes, tribes into families, families into genera, genera into species. Additional branchings could be indicated by similar terms where necessary. There was no attempt in Haeckel’s use of these terms to make them exactly or more than approximately equal in significance; such attempts were clearly futile and unimportant where the purpose was the exhibition of lines of descent, and where no natural equality of groups was to be expected cx hypothesi. Haeckel’s classification. of i866 was only a first attempt. In the edition of the Nati4rliche Schopfungsgeschic/ile published in 1868 he made a great advance in his genealogical classification, since he now introduced the results of the extraordinary activity in the study of embryology which followed on the publication of the Origin of Species. -

The pre-Darwinian systematists since the time of Von Baer had attached very great importance to embryological facts, holding that the stages in an animal’s development were often more significant of its true affinities than its adult structure. Von Baer had, gained unanimous support for his dictum, “Die Entwickelungsgeschichte ist der wahre Lichttrager für Untersuchungen uber organische Koroer” Thus J. MUller’s studies on the larval forms of Echinoderms and the discoveries of Vaughan Thompson were appreciated. Btit it was only after Darwin that the cell-theory of Schwann was extended to the embryology of the animal kingdom generally, and that the knowledge of the development of an animal became a knowledge of the way in which the millions of cells of which its body is composed take their origin by fission from a smaller number of cells, and these at last from the single egg-cell. kolliker (Developnient of Cephalo pods, 1844), Remak (Development of the Frog, 1850), and others had laid the foundations of this knowledge in isolated examples; but it was Kovalevsky,by his accounts of the development of Ascidians and of Amphioxus (1866), who really made

-zoologists see that a strict and complete cellular embryology of animals was as necessary and feasible a factor in the comprehension of their relationships as at the beginning of the century the coarse anatomy had been shown to be by Cuvier. Kovalevsky’s work aooeared between the dates of the Ge’nerelle Mort’holorie and the

Schopfungsgeschichte. Haeckel himself, with his pupil MikluchoMaclay, had in the meantime made studies on the growth from the egg of Sponges—studies which resulted in the complete separation of the unicellular or equicellular Protozoa from the Sponges, hitherto confounded with them. It is this introduction of the consideration of cell-structure and cell-development which, subsequently to the establishment of Darwinism, has most profoundly modified the views of systematists, and led in conjunction with the genealogical doctrine to the greatest activity in research—an activity which culminated in the work (1873—1882) of F. M. Balfour, and produced the profoundest modifications in classification.

Haeckel’s second pedigree is as follows:—

Phyla. Clades. Classes.

I iArchezoa.

I OvULARIA. ~ Gregarinae. 11ae~’1ee1’s

Protozoa. ~Infusoria. 1868

LBLA5TIJLARIA. ~ ~

ISPONGIAR. Porifera.

J ICoralla.

Zoophyta. ~ Ac~LEpvJ~a~ -~ Hydromedusae.

~, Ctenophora.

AcoaLouf. Platyhelniinthes.

Nemathelminthes.

Bryozoa.

Tunicata.

Vermes. C0EL0reATI. Rhynchocoela.

Gephyraca.

Rot atoria.

Annelida.

5 Spirobranchia.

cEPHALA. Lamellibranchja.

Mollusca. 1 5 Cochlides.

LEUCEPHALA. Cephalopoda.

I SAsterida.

Co1oissAcnI~ ? Crinoida.

Echinoderma. 1 s Echinida.

j~LIPOBRACHIA. ~ Holothuriae.

I CARIDES. , Crustacea.

IArachnida.

Arthropoda. 1 TRACHEATA. ~ Myriapoda.

I I Insecta.

ACRANIA. Leptocardia.

MON0RRHINA. Cyclostoma.

IPisces.

Vertebrata. ANAMNIA. ~ ~

~Amphibia.

IReptilia.

AMNIOTA -~ Ayes.

~Mammalia.

In representing pictorially the groups of the animal kingdom as the branches of a tree, it becomes obvious that a distinction may be drawn, not merely between the individual

Dendrimain branches, but further a.s to the level at which form

they are given off from the main stem, so that one distribu. branch or set of branches may be marked off as be- ~~ii of longing to an earlier or lower level than another set

of branches; and the same plan may be adopted

with regard to the clades, classes and smaller branches. The term “grade” was introduced by Ray Lankester (“ Notes on Embryology and Classification,” in Quart. Journ. Micr. Sci. 1877), to indicate this giving off of branches at a higher or lower, i.e. a later or earlier, level of a main stem.f The mechanism for the statement of the genealogical relationships of the groups of the animal kingdom was thus completed. Renewed study of every group was the result of the acceptance of the genealogical idea and of the recognition of the importance

i Sir Edwin Ray Lankester (b. 1847) was the eldest son of Edwin Lankester (1814—1874), a physician and naturalist (F.R.S. 1845), who became well known as a scientific Writer and lecturer, editor of the Quarterly Journal of Microscopical Science from 1853 to 1871, and from 1862, in succession to Thomas Wakley, coroner for Central Middlesex. Educated at St PaLl’s and both at Downing College, Cambridge, and Christ Church, Oxford, E. Ray Lankester obtained the Radcliffe Travelling Fellowship at Oxford in 1870, and became a fellow and lectuLer at Exeter College in 1872. From 1874 to 1890 he was professor of zoology and comparative anatomy at University College, London; and from 1891 to 1898 Linacre professor of comparative anatomy at Oxford. From 1898 to 1907 he was director of the Natural History Department of the British Museum. He was made K.C.B. in 1Q07. ~d. E. B.l.

of cellular embryology. On the one hand, the true method of arriving at a knowledge of the genealogical tree was recognized as lying chiefly in attacking the problem of the genealogical relationships of the smallest twigs of the tree, and proceeding from them to the larger branches. Special studies of small families or orders of animals with this object in view were taken in hand by many zoologists. On the other hand, a ~urvey of the facts of cellular embryology which were accumulated in regard to a variety of classes within a few years of Kovalevsky’s work led to a generalization, independently arrived at by Haeckel and Lankester, to the effect that a lower grade of animals may be distinguished, the Protozoa or Plastidozoa, which consist either of single cells or colonies of equiformal cells, and a higher grfde, the Metazoa or Enterozoa, in which the egg-cell by “cell division “ gives rise to two layers of cells, the endoderm and tic- ectoderm, surrounding a primitive digestive chamber, the archenteron. Of these latter, two grades were further distinguished by Lankester—those which remain possessed of a single archenteric cavity and of two primary cell-layers (the Coeleniera or Diploblastica), and those which by nipping off the archenteron give rise to two cavities, the coelom or body-cavity and the metenteron or gut (Coelornata or Triploblastica). To the primitive two-cell-layered form, the hypothetical ancestor of all Mctazoa or Enterozoa, Haeckel gave the name Gastraea; the embryonic form which represents in the individual growth from the egg this ancestral condition he called a “gastrula” The term “dibiastula, “ was subsequently adopted in England for the gastrula of Haeckel. The tracing of the exact mode of development, cell by cell, of the diblastula, the coelom, and the various tissues of examples of all classes of animals was in later years pursued with immense activity and increasing instrumental facilities.

Two names in connexion with post-Darwinian taxonomy and the ideas connected with it require brief mention here. Fritz Fritz Muller, by his studies on Crustacea (Für Darwin, Muller’s 1864), showed the way in which genealogical theory recaDif u- may be applied to the minute study of a limited group. lation. He is also responsible for the formulation of an important principle, called by Haeckel “the biogenetic fundamental law,” viz, that an animal in its growth from the egg to the adult condition tends to pass through a series of stages which are recapitulative of the stages through which its ancestry has passed in the historical development of the species from a primitive form; or, more shortly, that the development of the individual (ontogeny) is an epitome of the development of the race (phylogeny). Pre-Darwinian zoologists had been aware of the class of facts thus interpreted by Fritz Muller, but the authoritative view on the subject had been that there is a parallelism between (a) the series of forms which occur in individual development, (b) the series of existing forms from lower to higher, and (c) the series of forms which succeed ‘one another in the strata of the earth’s crust, whilst an explanation of this parallelism was either not attempted, or was illusively offered in the shape of a doctrine of harmony of plan in creation. It was the application of Fritz Muller’s law of recapitulation which gave the chief stimulus toembryological investigations between 1865 and 1890; and, though it is now recognized that “recapitulation “is vastly and bewilderingly modified by special adaptations in every case, yet the principle has served~ and still serves, as a guide of great value.

Another important factor in the present condition of zoological knowledge as represented by classification is the doctrine of degeneration propounded by Anton Dohrn. Lamarck believed in a single progressive series of forms, whilst Cuvier introduced

Do.hrn’s the conception of branches. The first post-Darwinian doctrine systematists naturally and without reflexiori accepted of degen- the idea that existing simpler forms represent stages cration. in the gradual progress of development—are in fact

survivors from past ages which have retained the exact grade of development which their ancestors had reached in past ages. The assumption made was that (with the rare exception of parasites) all the change of structure through which the successive generations of animals have passed has been one of progressive

elaboration. It is Dohrn’s merit to have pointed out i that this assumption is not warranted, and that degeneration or progressive simplification of structure may have, arid in many lines certainly has, taken place, as well as progressive elaboration and in other cases continuous maintenance of the status quo. The introduction of this conception necessarily has had a most important effect in the attempt to unravel the genealogical affinities of animals. It renders the task a more complicated one; at the same time it removes some serious difficulties and throws a flood of light on every group of the animal kingdom.

One result of the introduction of the new conceptions dating from Darwin was a healthy reaction from that attitude of mind which led to the regarding of the classes and orders recognized by authoritative zoologists as sacred institutions which were beyond the criticism of ordinary men. That state of mind was due to the fact that the groupings so recognized did not profess to be simply the result of scientific reasoning, but were necessarily regarded as the expressions of the “insight “ of some more or less gifted persons into a plan or system which had been arbitrarily chosen by the Creator. Consequently there

was a tinge of theological dogmatism about the whole matter.

.~

‘ ‘, ‘I

‘~ \ ~‘° ~-~t? ~

04

Sub-Grade S C~LONATA.

\ I

Sub-Grade A. CcELENTERA~

Grade 2. ENTCROZO~.

Grade I. PROTOZOA.

A genealogical tree of animal kingdom (Lankester, 1884).

To deny the Linna~an, or later the Cuvierian, classes was very much like denying the Mosaic cosmogony. But systematic zoology is now entirely free from any such prejudices, and the Linnaean taint which is apparent even in Haeckel and Gegenbaur may be considered as finally expunged. -

There are, and probably always will be, differences of opinion as to the exact way in which the various kinds of animals may be divided into groups and those groups arranged Lanin such an order as will best exhibit their probable kester’s genetic relationships. The main divisions which, system. writing in 1910, the present writer prefers, are those adopted in his Treatise on Zoology (Part II. ch. ii.) except that Phylum 17, Diplochorda (a name doubtfully applicable to Phoronis) is replaced by Podaxonia, a term employed by Lankester in the 9th edition of this encyclopaedia and now used to include a number of groups of doubtful but possible affinity. The terms used for indicating groups are “ Phylum “ for the large diverging branches of the genealogical tree as introduced by Haeckel, each Phylum bears secondary branches which are termed “classes,” classes again branch or divide into orders, orders into families, falnilies into genera, genera into species. The general purpose is to give something like an equivalence of importance to divisions or branches indicated by the same term, but it is not intended to imply that every phylum has the

Ursprung der Wirbelthiere (Leipzig, 1875); and Lankester, Degeneration (Londdn, f 880)

same range and distinctive character as every other, nor to make such a proposition about classes, orders, families and genera. Where a further subdivision is desirable without descending to the next lower term of grouping, the prefix “sub” is made use of, so that a class may be divided first of all into subclasses each of which is divided into orders, and an order into sub-orders each of which bears a group of families. The term “grade” is also made use of for the purpose of indicating the conclusion that certain branches on a larger or smaller stem of the genealogical tree have been given off at an earlier period in the history of the evolution of the stem in question than have o,thers marked off as forming a higher grade. Thus, to begin with, the animal pedigree is divided into two very distinct grades, the Protozoa and the Metazoa. The Metazoa form two main branches; one, Parazoa, is but a small unproductive stock comprising only the Phylum Porifera or Sponges; the other, the great stem of the animal series Enterozoa, gives rise to a large number of diverging Phyla which it is necessary to assign to two levels or grades—a lower, Enterocoela (often called Coelentera), and a higher, Coelomocoela (often called Coelomata). These relations are exhibited by the two following diagrams.

PARA(OA &~TEROZM

6ra\ /hI

Gr8de 8.METAZOA.

Grade A PROTOZOA.

Diagram showing the primary grades and branches of the Animal Pedigree.

$‘~%.i S

. ‘ I ‘~ — ~% \ \ \ I / ~

Grade B. COELO~1OCOELA.

40

.~. ‘~‘°fu.. rlen0P1~°

‘9?% \ / ~

N\/v

- Grade A. ENTEROCOELA.

Branch 8. ENTEROZOA.

Diagram to show the division of the great branch Enterozoa into two grades and the Phyla given off therefrom.

The Phylum Vertebrata in the above scheme branches into the sub-phyla Hemichorda, Urochorda, Cephalochorda and Craniata. The Phylum Appendiculata similarly branches into sub-phyla, viz, the Rotifera, the Chaetopoda and the Arthropoda. Certain additional small groups should probably be recognized as independent lines of descent or phyla, but their relationships are obscure—they are the Mesozoa, the Polyzoa, the Acanthocephala and the Gastrotricha.

We may now enumerate these various large groups in tabular form. -

BIONTA—PnY-rA, ANIMALIA.

GRADE A. Protozoa (various groups included).

GRADE B. Metazoa.

Branch a. Parazoa.

Phylum 1. P01UFERA.

Branch b. Enterozoa.

Grade 1. ENTEROCOELA.

Phylum 2. HYDROMEDUSAE.

3. SCYFHOMEDUsAE.

4. ANTH0ZOA.

5. CTENOI’HOPA.

Grade 2. COELOMOCOELA.

Phylum 6. PLATYELMIA.

7. NEMATOIDEA.

8. CHAETOGNATIIA

9. NEMERTINA.

10. Mou~usc.&.

ii. APPENDICULATA.

Sub-phyla: ROTIFERA, CHAETOPODA, ARTI’IROPODA.

12. EcHINODERMA.

13. VERTEBRATA.

Sub-phyla: HEMIcHORDA, UROCHORDA, CEPHALOCIIORDA, CRANIATA.

14. MEsozoA.

15. POLYZOA.

16. AcANTHOcEPHALA

17. P0DAx0NIA.

18. GASTROTRICHA.

A statement may now be given of the classes and orders in each group, as recognized by the writers of the CIassIvarious special zoological articles in the Eleventh fication Edition of the Encyclopaedia Britannica. These sub- adopted divisions of the larger groups are not necessarily in the

those theoretically approved by the present writer, ~A~1t but they have the valuable sanction of the individual

experts who have given special attention to different portions of the vast field represented by the animal kingdom.i

GRADE A. Protozoa (q.v.).

Phylum 1. Sarcodina (q.v.).

Class I. PROTEOMYXA (q.v.)

Class 2. RrnzoPoDA (q.v.).

Orders: Lobosa, Fslosa.

Class 3. HnLIozoA (q.v.).

Class 4. FORAMINIFERA (q.v.).

Orders: Nuda, A llogromidiaceae, Astrorhizidiaceae, Lituolidaceae, Miliolidaceae, Textulidar-idaceae, Cheilostomellaceae, Lagenidaceae, Globigerinidaceae, Rotalidaceae, Nummulidiaceae.

Insertae sedis. Xenophyophoridae (see FORAMINIFERA).

Class 5. RADI0LARIA.

Orders: Spumellaria (= Feripylaea), A cant haria (= A ctipylaea) , Nasselar-ia (= Monopylaea), Phaeodana (~= Tripylaea).

Class 6. LABYRINTHULIDEA (q.v.).

No Orders.

Class 7. MYXOMYcETES.

No Orders.

Phylum 2. Mastigophora (q.v.).

Class I. FLAGELLATA (q.v.).

Sub-class A. Rhizoflagellata.

Orders: Holomastigaceae, Rhizomastigaceae.

Sub-class B. Euflagellata.

Orders: Protomastigaceae, Chrysomonadaceae, Cra,ptomonadaceae, Chloromonadaceae, Euglenaceae, Volvocaceae.

Class 2. DINOFLAGELLATA.

Orders: Gymnodiniacear, Prorocentraceae, Peridiniaceae.

Class 3. CYSTOFLAGELLATA.

No Orders.

Phylum 3. Sporozoa (q.v.).

Class I. ENDOSPORA (q.v.).

Orders: Myxosporidia, Actinomyxidia, Sarcosponidia, Haplosporidia.

Class 2. ECTOSPORA (q.v).

Orders: Gregarlna (see GREGARINES), Coccidia (q.v.), Haemosponidia (q.v.).

Phylum 4. Infusoria (q.v.).

Class I. CILIATA.

Orders: Gymonoslomaceae, Tricho stomata, A spirotrichaceae, Spirotnicha, Heterotnichaceae, Oligo. trichaceae, Hypotrichaceae, Penitrichaceae.

Class 2. SUCTORIA.

No orders.

i It is to be noted that the terms used for designating categories in the classification are not always identical in this summary arid separate articles, as authors differ as to the use of these.

URADE B. Metazoa.

Branch a. Parazoa.

Phylum I. Porifera (se’~ SPONGES).

Sub-phylum I. Calcarea.

Class. CALCAREA.

Orders: Homocoela, Heterocoela. Sub-phylum 2. Non-Calcarea.

Class 1. MYx0sP0NGIDA,

Order: Myxospongida.

Class 2. TRIAXONIDA (= HEXAcTINELLIDA).

Orders: A mphidiscophora, Hexasterophora.

Class 3- TETRAXONIDA.

Sub-Class 1. Tetractinellida.

Orders: Homoscierophora, Astrophora, Sigmalophora.

Sub-class 2. Lithistida.

No Orders.

Sub-class 3. Monaxonellida.

Orders: Astromonaxonellida, Sigmatomonaxonellida.

Class 4. EUcERATO5A.

Order: Euceratosa.

Branch b. Enterozoa.

Grade I. ENTEROcOELA (see COELENTERA).

Phylum 2. Hydromedusae or Hydrozoa (q.v.).

Class. HYDROMEDUSAR, (g.e.).

Orders: Eleutheroblastea, Hydro’idae seu Leptolinae (Sub-orders: Anthoniedusae, LeptOmedusae), Hydrocorallinae, Graptolitoidea Trachylinae (Suborders: Trachomedusae, Narcomedusae), Sip/sonophora.

Phylum 3. Scyphomedusae (q.v.).

Class. ScYPIIOMEDUSAE.

Orders: cubomedusae, Stauromedusae, ~‘oronata, Disco phora.

Phylum 4. Anthozoa (g.e.).

Class. ANTHOZOA.

Sub-class I. Alcyonaria.

Orders: Stolonifera, Akyonacea, Pseudaxonia, Axifera, Stelechokskea, Coenothecalia.

Sub-class 2. Zoantharia.

Orders: Zoanthidea, Cereanthidea, A ntipat h-idea, Actiniidea (Sub-orders: Malacaainias and Scieraeliniae or Mad reporia).

Phylum 5. Ctenophora.

Class. CTENOPHORA.

Sub-class I. Tentaculata.

Orders: Cydi~~.idea, Lobata, Cestoidea.

Sub-class 2. Nuda.

No Orders.

Grade 2. COELOMOCOELA.

Phylum 6. Platyelniia (g.e.).

Class 1. PLANARIA (see PLANARIANS).

Order: Turbellarja.

Class 2. TEMNOcEPHALOIDEA (see appendix to PLANARIANS).

No Orders.

Class 3. TREMATODA (see TREMATODES).

Orders: Heterocotyless, Aspidocotylea, Malacocotylea.

Class 4. CESTODA (see TAPEWORMS).

Orders: Monozoa, Merozoa. Phylum 7. Nematoidea.

Class I. NEMATODA (see NEMATODE).

No Qrders.

Class 2. CHAETOSOMIDAE (see CHAETOSOMATIDA).

No Orders.

Class 3. DEsM05c0LEcIDA (g.e.).

No Orders.

Class 4. NEMATOMORPHA (q.v.).

No Orders.

Phylum 8. Chaetognatha (q.v.).

No Orders.

Phylum 9. Nemertina.

Class. NEMERT1NA (q.v.).

Orders: Protonemertini, Mesonemertini, Me/anemertini, Heteronemertini.

Phylum 10. Mollusca (q.v.).

Grade A. ISOPLEURA.

Class I. AMPH1NEURA (see CHITON).

Orders: Polyplacophora, Aplacophora.

Grade B. PR0RHI PIDOGLOSSOMORPHA.

Class 2. GASTROPODA (q.v.).

Sub-class I. Streptoneura.

Orders: Aspidobranchia, Pectin-i branchia.

Sub-class 2. Euthyneura.

Orders: Opisthobranchla, Pultnonata.

Class 3. SCAPHOPODA (qv).

No Orders.

Class 4. LAMELLIBRANCHIA (q.v.).

Orders: - Pro/obra.nchia, Fil’ibranchia, Eulamellihranchf a, Sep11 branch ía.

Grade C. SIpiloNopoDA.

Class 5. CEPHALOPODA (g.e.).

Orders: Tetrabranchia, Dibranchia. Phylum II. Appendiculata.

Sub-phylum 1. Rotifera (q.v.).

Class. ROTIFERA.

Orders: Asplanchnaceae, Mel’icertaceae, Trochosphaeraceae, ,Ploimoidaceae, Bciello’idaceae, Floscularaceae, Ploima, Seisonaceae.

Sub-phylum 2. Chaetopoda (g.e.).

Class I. POLYCHAETA.

Orders: Nereidiformia, Cryptocephala, Capitelliformia, Terebelliformia, Spioniformia, Scoleci~ formia.

Class 2. OLIG0cIIAETA.

Orders: .4phaneura, Limicolae, Moniligas/res, Terricolae.

Class 3. HIRuDINAE (see LEECH).

Orders: Rhynchobdellidae, Gnathobdellidae, A can/hobdellidae.

Class 4. MYZOSTOMIDA (g.e.).

No Orders.

Class 5. SACcOCIRRIDA.

No Orders.

Class 6. HAPLODRILI (g.e.).

No Orders.

Class 7. EcIlfuRofDEA (q.v.).

No Orders.

Sub-phylum 3. Arthropoda (q.e.).

Grade I. CERATOPHORA.

Class I. PERIPATIDEA (see PERIPATUS).

No Orders.

Class 2. CmLopoDA (see CENTIPEDE).

Sub-class I. Pleurostigma.

Orders: Geophilomorpha, Scolopendromorpiza, Craterostigmomorplus, Lithobiomorpha.

Sub-class 2. Notostigma.

Order: Scutigeromorpha.

Class 3. DIPLOPODA (see MILLIPEDE).

Sub-class 1. Pselaphognatha.

Order: Penicillata.

Sub-class 2. Chilognatha.

Orders: Oniscomorpha, Limacomorpha, Colobognatha, A scospermophora,Proterospermophora, Merochaeta, Opisthospermopliora.

Class 3. PAUROPODA (see MILLIPEDE).

No Orders.

Class 4. SYMPHYLA (see MILLIPEDE).

No Orders.

Class 5. HEXAPODA (g.e.).

Sub-class I. Apterygota.

Order: Aptera.

Sub-class 2. Exopterygota.

Orders: Derniaptera, Orthoptera, Plecoptera, Isoplera, Corrodentia, Ephemoptera, Odonata, Thysanoptera, Hemi ptera, A noplura.

Sub-class 3. Endopterygota.

Orders: Neuroptera, Coleoptera, Mecaptera, Tricho~tera, Lepidoptera, Diptera, Siphenaptera, Hymenoptera.

Grade 2. ACERATA.

Class I. CRUSTACEA (q.v.).

Sub-class I. Entomostraca (g.e.).

Orders: Branchiopoda (Sub-orders: Phyllopoda, Clad ocera, Branchiura), Ostracoda, Copepoda.

Sub-class 2. Thyrostraca (g.e.) = (Cirripedia). No Orders.

Sub-class 3. Leptostraca.

No Orders.

Sub-class 4. Malacostraca (g.e.).

Orders: Decapoda (Sub-orders: Braehyura, Macrum), .S’chilopoda (including Anaspides), Stomatopoda, Syinpoda (Cumacea), Isopoda (including Tanaidacea), A mphipoda.

Class 2. ARACHNIDA (g.e.).

Grade A. TRILOBITAE (see TRILOBITE).

(Orders not determined.)

Grade B. N0M0MERIsTIcA.

Sub-class I. Pantopoda.

Orders: Nympho-nomorpha, 4scorhynchomorpha, Pycnogonomorpha.

Sub-class 2. Eu-Arachna.

Grade a. Delobrancha (or Hydropneusta).

Orders: Xi/.~hosura, Gigantostraca.

Grade b. Embolobranchia (or Aeropneusta). Section. I’ectinifera.

Order: Scorpionidea. Section. Epectinata.

Orders: Pedipalpi, A raneae, Palpigradi, Solifugae, Pseudoscorpiones, Podogona, Op-iliones,

Rhynchostomi (Acari).

Class 3. TARDIGRADA (qv.).

No Orders.

Class 4. LINGUATALINA (see PENTASTOMIDA). No Orders.

Phylum 12. Echinoderma (see EcHIN0DERM5). Branch A. PELMATOZOA.

Class I. CYSTIDEA.

Orders: Ampiloridea, Carpoidea, Rlzombifera, Aporita, Diploporita.

Class 2. BLASTOIDEA.

Divisions Protoblastoidea, Eublastoidea.

No Orders.

Class 3. CRINOIDEA.

Orders: Monocycl’ica Inadunata, Adunata, Monocyclica Camerata, Dicyclica Inadunata, Flex ibilia, Dicyclica Carnerata.

Class 4. EDRIOASTEROJDEA.

No Orders.

Branch B. ELEIJTHEROZOA.

Class 1. HOLOTI-1UROIDEA.

Orders: A spidochirota, Dendrochirota. Class 2. STELLIFORMIA.

Sub-class 1. Asterida.

Orders: PhaneI-’ozonia, Crypiozonia. Sub-class 2. Ophiurida.

Orders: Streptophiurae, Zygophiurae, Cladophiurae.

Class 3. EcHfNoIriEA.

Orders: Bothriocidaroida, Melonitosda, Cystocidaroida, Cidaroida, Diademo-ida, Holectypoida, Spatangoida, Clypeasiroida.

Phylum 13. Vertebrata (q.v.).

Sub-phylum a. Hemichorda (q.v.).

Class. ENTEROPNEUSTA (see BALANOGLO5SUS). No Order.~.

Sub-phylum b. Urochorda.

Class. TUNIcATA (q.v.).

Orders: Larvacea, Thaliacea (Sub-orders: C’yclomyaria, Hemimyaria), Ascidiacea (Sub-orders:

A scidiae Simplices, A scidiae (‘orn positae, A scidiae Luciae).

Sub-phylum c. Cephalochorda (see AMPHIOXO5).

Class. CEPHALOCHORDA.

No Orders.

Sub-phylum d. Craniata.i

Class I. PIscEs (see IcHTHYOLoGy).

Sub-class 1. Cyclostomata (q.n.).

Orders: Myxinoides (Or Hyperotreti), Petronsyzontes (or Hyperoartii) -

Sub-class 2. Selachia or Elasmobranchii (see SELACHIANS).

Orders: Pleuropterygii, Acanthodii, Ichihyolomi, Plagiostomi, Hotocephali.

Sub-class 3. Teleostoma. -

Orders: Ganoidea, Crossopterygii, Dipneusti, Teleostei.

Class 2. BATRACIHA (ge.).

Orders: Stegocephalia, Apoda (or Peromela), Gaudata

- (or Urodela), Ecaudata (or Anura). Class 3. REPTILIA (see REPTILES).

Orders: A nomodontia, Chelonia, - Samopterygia, Ichthyopter-~’gia, Rhyncocephalia, Dznosauria, Crocod die, Ornithosaur-ia, Squamata.

Class 4. Avas (see BIRD and ORNITHOLOGY). Sub-class I. Archaeornithes.

No Orders.

Sub-class 2. Neornithes.

Division 1. Rat itae.

Orders: Struthiones, Rheae, Casuariae, Apteryges, Dinornithes, Aepyornithes.

Division 2. Odontolcae.

No Orders.

Division 3. Carinatae.

Orders: Ichthyornes, Colymb~formes, Splienisciformes, Procellariiformes, Ciconilformes, (Suborders: Steganopodes, Ardeee, Cicon’iae, Phoenicopteri). Anseriformes (Sub-orders: Palamedeae, Anseres), Faiconiformes (Sub-orders: Cathartae,

1 Craniata may be usefully divided into 3 grades: (a) Branchiata Ileterodactyla, which includes Pisces except Cyclostomes. (b) Branchiata Pentadactyla, which includes Batrachia. (c) Lipobranchia Pentadactyla, which includes Reptiles, Birds and Mammals.

A’ccipitres), Tinamiformes, Gall-if ormes (Sub orders:

Mesites, Turn-ices, Galli, Opisthocomi), Gruiformes, Charadri’iformes (Sub-orders: Linficolae, Lan, Pterocles, Columbee), Cuculiformes (Sub-orders:

Cuculi, Psittaci), Coraciiformes (Stib-orders: Goraciae, Str’iges, Gaprimulgi, Cypseli, Gel ii, Trogones, Pici), Passeriformes (Sub-orders: Passeres A nisomyodae, Passeres Diacromyodae).

Class 4. MAMMALIA (q.v.).

Sub-class 1. Monotremata (g.e.) (Prototheria).’ No Orders.

Sub-class 2. Marsupialia (g.e.) (Metatheria).

One Order: Marsh pialia.

Sub-orders: Polyprotodonta, Paucituberculata, Diprotodonta.

Sub-class 3. Placentalia (Monodelphia, g.e.; or Eutheria) -

Orders: Insectivora, Chiroptera, Dermopt~’ra, Edentate (Sub-orders: Xenarthra, Pholidota, Tubulidentata), Rodent-ia (Sub-orders: Duplicidentata, Simplicidentata), Tillodontia, Garnivora (Sub-orders:

Fissipedia, Pinnipedia, Creodonta), Getacea (Suborders: Archaeoceti, Odontoceti, Mystacoceti), Siren-ia, Ungulate (Sub-orders: Proboscidea, Hyracoidea, Barypoda, Toxcdontia, A mblypoda, Litopterna, A ncylopoda, Condylarthra, Perissodactyla, A rtiodactyla), Primates (Sub-orders: Prosirn see, A nthropoidea).

Phylum ‘4. Mesozoa (g.e.).

Class I. RiIoMnozoA.

No Orders.

Class 2. ORTHONECTIDA.

No Orders.

Phylum 15. Polyzoa (g.e.).

Class 1. ENTOPROcTA.

No Orders.

Class 2. ECTOPROCTA.

Orders: Gymnolaemata (Sub-orders: Tr-i75ostomata, Cry ptostomata, Cyclostomata, Cienostomata, Cheilostomata), Phylaclolaemata.

Phylum 16. Acanthocephala (g.e.).

Class. ACANTHOCEPIIALA.

No Ordecs.

Phylum 17. Podaxonia.

Class I. SIPUNCULOIDEA (g.e.).

No Orders.

Class 2. PRIAPULOIDEA (q.v.).

No Orders.

Class 3. PHORONIDEA (g.e.).

No Orders.

Class 4. PTEROBRACHIA (g.e.).

No Orders.

Class 5. BRACHIOPODA (g.e.).

Sub-class 1. Ecardines (Inarticulata).

Orders: Atremata, Neotremata.

Sub-class 2. Testicardines (Articulata).

Orders: Protremata, Telotremata. Phylum 18. ,Gastrotricha (q.v.).

Class. GASTROTRICHA.

Sub-orders: Ichthydina, Cepodina. (Possibly Kinorhyncha (qv.) with only Echinoderes is ‘to be placed here).

See also

• cladistics
• evolutionary tree
• Linnaean taxonomy
• phylogenetic tree
• phylogeny
• scientific classification
• systematics
• taxonomy

Much of the contents of this article are taken from the 1911 Encyclopaedia Britannica.