n] BIOLOGICAL FOUNDATIONS 45 



and nucleus, of two other cells, these are technically 

 known as the gametes, and their product, the fertilized 

 ovum, as the zygote. These two cells have come from 

 two separate individual persons (one male and one 

 female) and their cell-ancestors have been firmly 

 built into the fabric of those individuals' bodies. 



This merging of two cells and their two in- 

 dividualities in one (the exact reverse of fission) is 

 the essential sexual act, and is usually known as the 

 conjugation of the two cells. It will be considered 

 more fully later (p. 71); here it does not concern us, 

 for, as Weismann and others have conclusively proved, 

 reproduction and conjugation are in their origin 

 totally distinct from each other. In all the Metazoa, 

 however, conjugation is always connected with repro- 

 duction, so that the fusion of two cells always implies 

 the production of a new individual. In ourselves, and 

 all other Vertebrates, the converse also is true, that 

 the production of a new individual always implies the 

 previous fusion of two cells reproduction, in other 

 words, is always sexual: but in very many of the 

 lower Metazoa, though conjugation leads to repro- 

 duction, reproduction may occur independently of 

 conjugation. Two examples of this asexual reproduc- 

 tion have been seen in budding and in fission. 



Thus the complication introduced by the fusion 

 of the two gamete-cells into the otherwise unvaried 

 succession of cell-divisions does not really affect the 



