Volvox

Volvox is one of the best known genera of green algae, and is the culmination of the evolution of spherical colonies. Each Volvox is composed of on the order of a thousand cells, each a biflagellate similar to Chlamydomonas, interconnected and arranged in a hollow sphere, with a distinct anterior and posterior. Asexual colonies consist of somatic or vegetative cells, which do not reproduce, and gonidia, which reproduce, reproduction being a process of longitudinal division. Sexual or oogamous colonies contain, as well as somatic cells, ova (non-motile female cells) or spermatozoa (small, motile male cells) or a mixture of the two. These cells, near the back of the colony, develop into new colonies, initially with the flagella directed inwards and held within the parent. Eventually the parent bursts and the daughter colonies evert.

Volvox is found in ponds and ditches, and even in shallow puddles. The most favorable place to look for it is in the deeper ponds, lagoons, and ditches which receive an abundance of rain water. It has been claimed that where you find Lemna, you are likely to find Volvox; and it is true that such water is favorable, but the shading is unfavorable. Look where you find Sphagnum[?], Vaucheria, Alisma, Equisetum fluviatile, Utricularia, Typha, and Chara, Dr. Nieuwland reports that Pandorina[?], Eudorina and Gonium are commonly found in summer as constituents of the green scum on wallows in fields where pigs are kept. The flagellate, Euglena, is often associated with these forms. If you have a culture in the laboratory, do not throw it out when the culture disappears, because new coenobia are likely to develop from the oospores.

For collecting, use "bolting cloth" or "bolting silk" of the finest mesh available. With a piece of thin cloth about 15 cm. square, laid over an ordinary coffee strainer, you can pour through about 4 liters of water in a minute. In this way you will secure all the Volvox in about a barrel of water in half an hour. Eudorina may be collected in the same way. Smaller members of the Volvox family like Pandorina, Gonium, and Chlamydomonas are too small to be held by the cloth; but if material is very abundant, the water goes through faster than the organisms and you will soon have many times as much material in a bottle as you could get by dipping. Many small organisms are effectively collected in this way, even when they are so small that most of them pass through the cloth.

Material of Volvox and all the Volvocales may be fixed in the corrosive sublimate-acetic mixture [1], used hot-85° C. If material is to be stained and mounted whole, use the aqueous mixture; if it is to be imbedded and cut, use the alcoholic. For mounting whole, stain in iron-alum haematoxylin, or in Magdala red and anilin blue, following the Venetian turpentine method. A few bits of broken cover-glass, placed among the colonies, will prevent crushing.

[1] corrosive sublimate is mercuric chloride (HgCl₂). corrosive sublimate-acetic is a mixture of mercuric chloride (2 g), glacial ethanoic acid (2 cm³) and water (100 cm³).