Later Additions tip to the year 1892. 41 



consist of pure germ-plasm (i. e., of idio-plasm-B 

 belonging to the first ontogenetic stage), and one half 

 of this is next got rid of by the second segmentation 

 in the form of the second polar body. Therefore, 

 according to the theory and so far as the problems 

 of heredity are concerned, we need not any further 

 trouble ourselves about the first polar body. But it 

 will at once be seen that by the interpretation which 

 Weismann puts upon the second polar body, and 

 also, of course, upon the extrusion of some of its 

 nuclear matter by the male cell, he meets both the 

 difficulties against his theory of germ-plasm which 

 we are now engaged in considering. 



That he thus meets the second of those difficulties — 

 i. e., concerning the otherwise perpetual accumulation 

 of germ-plasm — is evident without explanation. That 

 he likewise meets the first — i. e., concerning the non- 

 resemblance of individuals born of the same parents — 

 is scarcely less evident. For it is hardly conceivable 

 that such a complex mass of germ-plasms as the 

 nucleus of a fertilized ovum must be could ever 

 present in any two eggs precisely the same propor- 

 tional representation of the " carriers of heredity," 

 after one half of each set had been thus discharged 

 from each egg. Therefore, if the second polar body 

 removes from each egg one half of the ancestral germ- 

 plasms, " every egg will contain a somewhat different 

 combination of hereditary tendencies, and thus the 

 offspring which arise from the different germ-cells of 

 the same mother can never be identical 1 . 



Such, then, is Weismann's theory of the physio- 



1 In the case of identical twins, both are probably always produced 

 from the same ovum. 



