THALJ.OPHYTES 
FIG. 29. Volvox : the large globular colony 
composed of small vegetative cells connected by 
strands of cytoplasm, two large colony-forming cells, 
twelve) much larger ones 
which divide to form new 
colonies. These large 
colony-forming cells are 
derived from the smaller 
cells and have been called 
gonidia, a very inappropri- 
ate name. 
The sexual reproduction 
is much as in Eudorina, 
but the eggs become much 
larger than the ordinary 
cells and lose their cilia. 
The sperms, produced by 
the division of certain 
cells, are elongated, yellow, 
and biciliate. Fertilization 
occurs in the cavity Ol the and numerous oospores with rough walls. 
colony (fig. 31), and the 
resulting oospore is a resting, vprotected cell (fig. 32). Upon germina- 
tion, there comes from the oospore a group of ciliated cells (equivalents 
of zoospores) that represent a new colony. 
In this so-called Volvox colony differentiation has resulted in four 
distinct kinds of cells: ciliated vegeta- 
tive cells, colony-forming cells, eggs, 
and sperms. 
Conclusions. A summary of the 
features of the Volvocales may be 
stated as follows: The forms range 
from isolated cells to complex spheri- 
cal colonies, all the ordinary cells 
being ciliate; a new colony is formed 
from the division of a single mother 
cell; sexual reproduction is present, 
advancing from isogamy to heter- 
ogamy, that is, from the origin of sex 
FIGS. 30-32. Volvox: 30, periph- to the differentiation of sex. Volvox 
eral cells of the colony (after WEST); . i < -n- 
31, an egg surrounded by sperms; 3*. an and its colony-forming allies are to 
oospore with heavy wall. be regarded as specialized forms, and 
