THALLOPHYTES 29 
each one of which produces a single very large egg, conspicuously filled 
with reserve food, and develops a perforation which the sperms enter. 
Still other cells of the filament divide, the daughter cells not elongating, 
thus producing a short row of small cells, the antheridia, within each 
one of which one or two sperms are developed (fig. 77). The sperms 
are much smaller than the zoospores, but they have the same crown of 
cilia, and this evident relationship between spore and sperm is constantly 
75 
76 
FIGS. 74-76. Oedogonium: 74, large zoospore forming within the cell, including all 
the contents; 75, zoospore escaping from cell; 76, zoospore freed from its membrane. 
74, after PRINGSHEIM; 75, 76, after HIRN. 
appearing. In this case the oogonia and antheridia are distinct from 
the vegetative cells, but still they are transformed vegetative cells. The 
sperms escape from the antheridia, swarm about the oogonia, enter 
them through the perforation, and fertilize the eggs. Although several 
sperms may enter an oogonium, only one is concerned in the act of fer- 
tilization, the essential feature of which seems to be the fusion of the two 
nuclei. The oospore is a heavy-walled cell, which upon germination 
produces four zoospores, each one of which gives rise to a new filament 
(figs. 80-82). 
In the form of Oedogonium just described, the oogonia and antheridia 
occur in the same filament, but in certain species they occur on different 
