20 ANIMAL FORMS 
from place to place. As just indicated, some individuals 
lack the flagella, and their subsequent careers show them 
to be of a peculiar type. Sooner or later each undergoes 
a series of divisions form- 
ing a little globe of cells, 
which migrates into the in- 
terior of the parent sphere 
and develops into a new 
colony. Within a short time 
the walls of the parent 
break, liberating the im- 
prisoned young, which con- 
tinue-the existence of the 
species while the parent or- 
ganism soon decays. 
Under certain circum- 
stances, instead of develop- 
ing colonies by such a meth- 
od, some of the cells may 
store up food matters and 
become eggs, while others, 
known as sperm-cells, de- 
velop a flagellum, and sep- 
arating from the colony 
swim actively in the sur- 
rounding water, where each 
finally unites with an egg. 
This union, like that of the 
two individuals in Vorticel- 
la (Fig. 8, 6, c), results in 
Fie. 10.—A, Volvox minor, entire colony the power of division, and 
(from Nature). B, C, and D, reprodue- the egg enters upon its de- 
aealied Volvox globator. All highly velopment, diva ding again 
andagain. The cells so pro- 
duced remain together, form a sphere, and finally develop 
a Volvox colony. 
