THE EVOLUTION OF SEX 15 



can at least see how the process once begun might be 

 utilized in the building up of new combinations ; and 

 t o-day e vo lution has come to mean not so much a 

 study of the origination of new characters as the method 

 by which new characters become established after they 

 have appeared. 



THE BODY AND THE GERM-PLASM 



As I have said, it is not unusual to speak of the uni- 

 cellular animals and plants as sexual individuals, and 

 where one of them is larger than the other it is some- 

 times called the female and the smaller the male. But 

 in many-celled animals we mean by sex something 

 different, for the term applies to the body or soma, and 

 not to the reproductive cells at all. The reproductive 

 cells are eggs and sperm. It leads to a good deal of 

 confusion to speak of the reproductive cells as male 

 and female. In the next chapter it will be pointed out 

 that the eggs and sperm carry certain materials ; and 

 that certain combinations of these materials, after fer- 

 tilization has occurred, produce females ; other combi- 

 nations produce males ; but males and females, as such, 

 do not exist until after fertilization has taken place. 



The first step, then, in the evolution of sex was taken 

 when colonies of many cells appeared. We find a 

 division of labor in these many-celled organisms ; the 

 germ-cells are hidden away inside and are kept apart 

 from the wear and tear of life. Their maintenance 

 and protection are taken over by the other cells of the 

 colony. Even among the simplest colonial forms we 

 find that some colonies become specialized for the pro- 

 duction of small, active germ-cells. These colonies 



