SEX AND THE INDIVIDUAL 183 



The striking fact that all the higher animals 

 multiply through the union of cells coming from two 

 distinct sexes is in contrast to the fact that the 

 lowest forms of life multiply by much more direct 

 and simple means, such as budding or fission. This 

 contrast in methods and their results in itself suggests 

 that the relatively complex sexual means of repro- 

 duction are, in some way, necessary to yield the 

 highest types of animal development, and such an 

 inference is well borne out by facts. It is almost 

 self-evident that the fusion of male and female cells 

 serves the purpose of bringing together in one 

 organism a far wider range of hereditary possibilities 

 than would be possible with any simpler system of 

 reproduction. It is an interesting circumstance that 

 some degenerating species of animals, such as bar- 

 nacles, exhibit exceptional complexity in the repro- 

 ductive processes. The reason for this complexity 

 appears to lie in the fact that the animals in question 

 have very many eggs of extremely small size, thus 

 calling for special and complex reproductive mechan- 

 isms for their disposal. Instances of this sort in no 

 wise invalidate the general statement that the change 

 from the simpler methods of reproduction to the 

 more complex forms of sexual reproduction mark an 

 advance essential to the evolution of progressively 

 higher types of animal mechanism. 



The process of fertilization is one of rejuvenation of 



