68 REPRODUCTION 



the sex of the cells seems to be stamped on the organs 

 that produce them. An experienced biologist can usually 

 tell which sex an organ represents, even though he has 

 never seen the organism before. The sex quality of the 

 organ becomes as marked as that of the gametes 

 themselves. The gametes are specialized. The organ 

 that produces them becomes equally so. 



4. Specialization of the Parents. Where the gametes 

 are alike, there is no difference in the organs that produce 

 them, and the parents are all alike. But a step higher up 

 we also find different kinds of gametes, produced in 

 different types of organs, but all in one kind of parent. 

 One of the very best illustrations of this in the animal 

 kingdom is the common earthworm. In certain segments 

 of its body-cavity it produces sperms; in other segments 

 it is producing eggs. Each earthworm must perform all 

 the duties of father and mother. 



But in the very same group of worms, in some of the 

 marine forms, we find a surprising difference. In these 

 one animal produces one or the other kind of gametes; 

 not both. If one segment of these worms produces 

 sperms, all the segments produce sperms, and the whole 

 animal is a male. Other worms produce eggs only. These 

 eggs and sperms from different animals must unite. Here 

 we have sex in the gametes; sex in the organs that produce 

 the gametes; and sex in the individual that bears the 

 organs. Beginning with the differentiation of eggs and 

 sperms, differentiation of sex has worked back into the 

 parents which produce them. This is the first time that 

 we have found organisms permanently and wholly male 

 (father) and female (mother) in a strict sense. In some 

 animals in which sex is distinct the differences between 

 males and females cannot be detected externally, though 

 there are internal differences. 



5. Further Differentiations of Parents. This difference 

 in the sex organs is the most fundamental difference in 



