Sex as an Adaptation 431 
Now, in certain cases of parthenogenesis, it has been found 
that one of the polar bodies may not be given off, but, remain- 
ing in the egg, its nucleus reunites with the egg nucleus, and 
thus takes the place of the spermatozoon, which does exactly 
the same thing when it fertilizes the egg, z.c. the nucleus of 
Fic. 7.— Diagram showing the maturation of the spermatozoon. 
the spermatozoon unites with the nucleus of the egg. This 
fact in regard to the action of the polar body in fertilization 
is not as surprising as appears at first sight, for if each of the 
polar bodies is equivalent to a spermatozoon, the fertilization 
of the egg by one of its own polar bodies conforms to theory. 
There is a considerable body of evidence showing that 
in many eggs at one of the two maturation divisions the 
