GREAT STEPS IN EVOLUTION 89 



This is an economical improvement on the 

 method of starting a new life by a sexual over- 

 growth or by the liberation of buds. More- 

 over, the peculiarity of true germ-cells is that 

 they do not share in building up the " body," 

 and that they retain an organization contin- 

 uous in quality with the original germ-cell 

 from which the parent arose. They are thus 

 not very liable to be tainted by the mishaps 

 which may befall the " body " which bears 

 them. And again, in the life-history of the 

 germ-cells, and in the mingling of two of them 

 of different experiences in fertilization, there 

 is apparently opportunity for new organic 

 permutations and combinations variations 

 in short. Perhaps there is some subtler 

 advantage still in the process which ensures 

 that each new life usually begins in a unifica- 

 tion of two inheritances. 



The third aspect of the problem is that 

 most multicellular organisms are males or 

 females. The former liberate male elements, 

 which are usually actively motile; the latter 

 form, and usually liberate, more passive egg- 

 cells or ova. In the lower reaches of the 

 animal kingdom there is seldom much differ- 

 ence between males and females; indeed, it is 

 often impossible to distinguish the two sexes 

 without a microscopic examination of the 



