228 
POPULAK SCIENCE KEVIEW. 
time that the gynogonidia have matured into oogonia, and their 
protoplasmic contents into oospheres, the movements of the 
vibratile cilia attached to the antherozoids begin to set the 
whole antheridium in motion, in the positions indicated in fig. 
1, a, a 2 ; the antheridium soon breaks up, and the separate 
antherozoids are seen in rapid independent motion within the 
gelatinous envelope of the antheridium (fig. 1, a 3 ), which they 
ultimately break through, and then move about rapidly in all di- 
rections within the cavity of the mother-colony. Their movements 
are described by Cohn as being remarkably beautiful, the con- 
stant curvings of the elongated neck of the antherozoid being 
compared by him to those of the neck of a swan. They assemble 
in large numbers round the oogonia, and some of them finally 
penetrate through their gelatinous envelopes (fig. 1, 6 4 , fig. 7), 
and coalesce with their protoplasmic contents or oospheres. The 
fertilised oosphere is now an oospore, and developes a new cell- 
wall, the epispore, which is at first smooth, but afterwards 
covered with conical elevations, giving a section of it a stellate 
appearance (fig. 8). A second perfectly smooth membrane, 
the endospore, is subsequently formed within the first. The 
chlorophyll gradually disappears, and is replaced by an orange- 
red pigment dissolved in oil, so that the mature oospore, while 
still enclosed within the mother-colony, is of a bright red colour, 
giving the red tinge which Volvox often presents, even to the 
naked eye, at certain periods of the year. Individuals containing 
oospores still enveloped in their spiny coatings were described 
by Ehrenberg as a distinct species, under the name of V. stellatus. 
The number of sexual reproductive cells in a colony of Volvox 
varies greatly ; Cohn has observed five or more male and about 
forty female cells. 
Soon after the oospore reaches maturity, the mother-colony 
breaks up, single cells escaping from the combination and swim- 
ming about freely in the water ; their further history is unknown ; 
while the oospores fall to the bottom and there hibernate. Their 
further development has only been observed by Cienkowski, who 
states that the contents of each spore break up into eight spheres 
which ultimately swarm out. 
Ehrenberg described two species of Volvox , V. globator and 
V. stellatus , both of which he considered to be infusorial ani- 
malcules. These have been determined by Cohn to be different 
stages of the same species, the former in its parthenogenetic, 
the latter in its sexually reproductive condition ; Ehrenberg’s 
Sphcero8ira Volvox is also another form of the same species. 
His Volvox aureu8 , and Stein’s V. minor , are considered by 
Cohn to form a distinct sub-species of V. globator , differing 
from the typical form in the colonies being of a smaller size, and 
dioecious instead of monoecious, and in the epispore of the 
