Later Additions tip to the year 1892. 45 



reasons which he assigns for this rejection of it are 

 adequate. 



First, he says that if this were the way in which the 

 superfluous germ-plasm of each generation were got 

 rid of, far too much provision has been made for the 

 purpose, — seeing that the practically indefinite number 

 of nuclear divisions which the immature germ-cells 

 undergo would cause a much " greater decrease of 

 the ancestral idio-plasms of each than could afterwards 

 be compensated by the increase due to fertilization." 

 But this rejoinder is of cogency only if it be supposed 

 that at each nuclear division of an immature ovum, 

 "the ancestral idio-plasms" (germ -plasm) are in- 

 capable of the power of self-multiplication which soon 

 afterwards becomes one of its most essential characters. 

 Why, then, should we suppose this substance to be 

 totally incapable of increase in the multiplying ova of 

 ontogeny, when at the same time we are to suppose 

 the same substance capable of any amount of increase 

 in the multiplying ova of phylogeny ? To this obvious 

 question no answer is supplied: in fact the question 

 is not put. 



Secondly, Weismann says that in parthenogenetic 

 ova only one polar body is extruded. This he regards as 

 equivalent to the first polar body of a fertilizable ovum 

 (i. e., as composed of ovogenetic nuclear substance) ; 

 and hence he argues that the second polar body 

 of a fertilizable ovum must be regarded as composed 

 Oi germ-plasm. But even supposing that he is right 

 as to the fact that parthenogenetic ova invariably 

 extrude but one polar body, his argument from this 

 fact would only be available after we had already 

 accepted his view touching the character of the 



