YOLYOX GLOBATOR. 
227 
breaks up on its third segmentation. The young colonies com- 
plete their growth in a few days, attaining a diameter of from 
00*10 to 00*15 mm., and have by this time absorbed the greater 
part of the chlorophyll and starch of the mother-colony. 
The sexual reproductive cells, male and female, are very few 
in proportion to the sterile cells. While the non-sexual repro- 
duction by parthenogonidia takes place during the whole year, 
the sexual cells are apparently formed only in the autumn. The 
two kinds are found either in the same or in different colonies, 
establishing the classification of the genus into monoecious and 
dioecious sub-species, as first pointed out by Cohn. Fig. 1 
represents a monoecious colony. The two modes of reproduction 
do not take place simultaneously in the same colony, the sexual 
generation forming the close of a longer or shorter series of non- 
sexual generations. Volvox presents, in fact, one of the earliest 
instances in the ascending series of the phenomenon known as 
alternation of generations, which attains its highest development 
in plants in the Vascular Cryptogams. The female cells (gynogo- 
nidia of Cohn) are at first undistinguishable from the parthenogo- 
nidia, but are much more numerous. On their first appearance they 
are about three times the size of the sterile cells ; their protoplasm- 
body increases rapidly, and becomes of a dark green colour from 
abundance of chlorophyll. They have at first a frothy appear- 
ance (fig. 1, b) from the formation of vacuoles, but afterwards 
appear to be filled with protoplasm ; and they are now at once 
distinguishable from the parthenogonidia by their never dividing. 
They soon become flask-shaped (fig. 1, b 2 ), their narrow end 
touching the periphery of the sphere, and the larger end hanging 
free into the cavity. When ready for impregnation they round 
themselves off into a spherical form (fig. 1, 6 3 ), and may then be 
designated oospheres, each being enveloped in a gelatinous 
membrane or oogonium. The male cells, or androgonidia, present 
at first a still closer resemblance to the parthenogonidia, since, 
when they have attained about three times the size of the sterile 
cells, they begin to divide ; but they are of a lighter colour, from 
containing a smaller quantity of chlorophyll. The divisions also 
take place only in two instead of in three directions, thus de- 
veloping, not into a sphere, but into a plate of cells. They 
ultimately resolve themselves into a bundle of naked primordial 
cells (fig. 1, a ), each consisting of a thicker but elongated body, 
in which the chlorophyll has been transformed into a reddish 
yellow pigment, and of a long colourless beak, to the base of which 
are attached two very long vibratile cilia, and where also is a red 
corpuscle or eye-spot (see figs. 4, 5, 6). The whole androgoni- 
dium may now be considered as an antheridium enclosed in a 
gelatinous envelope, each of the naked protoplasmic bodies 
being a motile antherozoid or spermatozoid. About the same 
