REPRODUCTION 423 
fact suggests that the sexual cells have been derived from 
asexual ones, and are a later development, therefore, in the 
history of the race. 
The more complete differentiation of the gametes into 
male and female can be observed among several of the 
families of the Algw. In some species of Ectocarpus and 
Cutlerva the gametes are much like those of Ulothriz, but 
some are smaller than the others. The larger ones come 
to rest soonest, and lose their cilia; one of the smaller 
more motile ones then fuses with each of the larger. We 
can in this case speak of the larger as female and’ the 
smaller as male. The differentiation is still very rudi- 
Fic. 170.—Ooconium or Fucus, con- Fie. 171,—Awn Oosprere or Fucus 
TAINING EIGHT OOSPHERES. (After SURROUNDED BY ANTHEROZOIDS 
Thuret.) (After Thuret.) 
mentary, as in the event of no fusion taking place the 
female cell can still develop into a new plant. 
The most complete differentiation of the gametes can 
be traced in the higher members of the Alge. The females 
become larger and cease to develop cilia, the males remain 
small and motile. The former are then called oospheres 
and the latter antherozotds or spermatozoids. A good 
example of this stage of differentiation is afforded by Fucus 
(figs. 170 and 171). 
The structures or organs in which the sexual cells of 
these plants are formed are known as gametangia. When 
the gametes are distinctly male and female the gametangia 
