THE EVOLUTION OF SEX 47 



be more or less changed in connection with 

 its new function. Some investigators, such 

 as Tandler and Grosz and Kammerer, have 

 gone the length of maintaining that all sex- 

 characters have arisen from the transforma- 

 tion of species-characters. " Just as in the 

 primitive Metazoon body the cells lying next 

 the gametes came by change of function into 

 the service of reproduction, so it may have 

 been that more distant cell -complexes, which 

 had already reached some degree of structural 

 differentiation and subserved other functions, 

 suffered partial or even total loss of their 

 original function, and became auxiliary to 

 reproduction." 



SEX DIMORPHISM. In many of the simple 

 backboneless animals, the two sexes are 

 practically identical in appearance, and ex- 

 hibit no definite sex-behaviour. Thus without 

 a microscope it is often impossible to tell a 

 male starfish from a female, or a female from 

 a male sea-urchin. Nor can we see that the 

 one sex is attracted to the other. The 

 fertilisation of the eggs is more or less hap- 

 hazard, but it must be noted that large num- 

 bers of individuals are found living together, 

 and that the males and females become 

 mature about the same time. Both ova and 

 spermatozoa are set adrift in the sea, and as 

 there are thousands of sperms for every ovum 

 the chance of fertilisation is much greater 

 than would at first sight appear likely. 

 Moreover, from within a short distance there 

 is a " chemotactic " attraction of the sperma- 

 tozoa to the ova (see Fig. 9). 



It should be noted that animals like sea- 



