REPRODUCTION. 667 



takes up : he states, namely, with regard to the ova of animals, 

 that the process of development of a normal ovum is pre- 

 cisely the same as that of a parthenogenetic ovum. If this 

 be so, why is the parthenogenetic ovum capable, and the 

 normal ovum incapable, of independent germination ? The 

 answer to this question is by no means definite. Weismann 

 admits that a reproductive cell is only capable of inde- 

 pendent germination when it contains a certain proportion 

 of reproductive substance. Clearly then, a parthenogenetic 

 ovum must contain more reproductive substance than a 

 normal ovum. But how is this difference to be accounted 

 for ? If the process of development has been the same, there 

 is no ground for assuming that the parthenogenetic ovum 

 contains ab initio more reproductive substance than the 

 normal ovum, and we are therefore led to suggest that the 

 reproductive substance in the parthenogenetic ovum may 

 have been increased by growth. But Weismann brings for- 

 ward arguments to prove that a sufficient increase cannot be 

 attained in this way. There is therefore no means whatever 

 of accounting for the difference between a parthenogenetic 

 and a normal ovum. 



Weismann appears to have been conscious of this diffi- 

 culty, for he goes on to say that the capacity of the ovum for 

 subsequent development does not solely depend upon the 

 mass of nucleus, that is, upon the amount of " reproductive 

 substance" in it, but upon certain internal conditions which 

 he does not define. And yet he asserts that the determining 

 cause of the development of the fertilised ovum is the sudden 

 doubling of the mass of nucleus. 



There is a matter of fact bearing upon this subject to 

 which we will briefly refer. If, as Weismann insists, the 

 extrusion of the polar body simply means the extrusion 

 of the histogenic nucleoplasm, it is a fair inference that the 

 nucleus of a gamete and that of the corresponding polar 

 body will have different reactions. It has been already 

 pointed out that the generative and vegetative nuclei in a 

 pollen- tube stand to each other in the relation of sexual and 

 polar nucleus. Now Strasburger has observed that there is 



