44 EVOLUTION OF PLANTS 
and soon assume all the characters of the parent- 
cell. 
In the more specialized forms, like the water-net 
(Fig. 7, B, C), which may be said to bear somewhat 
the same relation to the lower forms that Volvox does to 
the lower Volvocinex, the young individuals become 
united into a colony of definite form. The zodspores, 
or ciliated, reproductive cells, remain within the mother- 
cell, where they grow together into a small net which 
is set free by the gradual dissolution of the wall of the 
mother-cell. The sexual cells, however, are ejected 
from the mother-cell, and unite two and two into 
spores which, in time, after several intermediate stages, 
give rise to several new nets. In nearly all these 
forms, both non-sexual and sexual cells show a rever- 
sion to the primitive biciliate cell, resembling closely 
in its structure the individual cells of the lower 
Volvocinee from which these forms have presumably 
originated, but having only a very limited period of 
independent, active existence. 
Within the Protococcacee we find considerably less 
specialization than exists among the Volvocineer. Thus 
none of them can be properly considered as truly multi- 
cellular, for such forms as the water-net and its allies are 
really colonies of originally unicellular units, and all 
the individuals of the colony are alike. So, too, sexual 
cells, when they exist at all, are of the simplest type, 
with no difference between the male and female cells 
or gametes, which closely resemble the non-sexual 
zoospores. 
As the lower Protococcacee are very intimately con- 
nected with the series of green algz which are the un- 
