28 HEREDITY 



If the germ-plasm is continuous or immortal, 

 then the individual body does not produce it, but 

 is its host. Hence we are led to inquire into the 

 relations between the one and the other. Does the 

 germ-plasm affect the body that carries it ? Does 

 the body affect the germ- plasm ? The second of 

 these questions will later be considered. The first 

 is not material to our subject. 



Let us now recall the fact that the germ-cells, or 

 gametes, are male and female, for this is evidently 

 a fact of very great importance. But it is not an 

 essential fact nevertheless, for we find that the 

 female gamete may develop and give rise to an 

 individual without the interposition of the male. As 

 this is the simpler case it falls to be considered first. 



Reproduction by means of a single (female) germ- 

 cell is called parthenogenesis, the nearest English 

 equivalent of which is virgin-birth. This develop- 

 ment of the female gamete without fertilisation by 

 the male is found in many very lowly groups of the 

 animal kingdom. Furthermore, it can be initiated 

 by artificial modification of the environment of the 

 ovum. Our business here, however, is to discuss 

 this matter only in so far as it bears on heredity. 

 If, then, we consider all the known cases of natural 

 parthenogenesis, and all the successful attempts to 

 induce parthenogenesis, what do we find as to the 

 occurrence of heredity and variation ? The case is 

 simpler than that of bi-parental reproduction, and 

 should be more intelligible. 



Our concept of the " continuity of the germ- 

 plasm " fully prepares us to understand the fact of 

 heredity in cases of parthenogenesis. We have 



