2 8o RECENT CYTOLOGY 



upon a common assumption, which is now shown by 

 Mendel's discovery to have been unfounded. This is 

 the assumption that all ancestors of the same degree 

 e.g., grandparents make a substantially equal con- 

 tribution to the hereditary qualities of the offspring. 

 Mendel has shown that in the case of particular 

 hereditary characteristics this is not the case. 



But if we venture to criticise Weismann's conception 

 in the light of more recent knowledge, it must not be 

 forgotten that biology, and especially modern cytology, 

 owes a great debt to Weismann. To Weismann is due 

 the conception of the isolation of the germ-cells from 

 somatic influences, a view which is in complete accord- 

 ance with the Mendelian view of the inheritance of 

 definite characters. And it was Weismann who first 

 emphasized the belief that the chromosomes represent 

 those parts of the nucleus which are specially concerned 

 in the process of heredity. These conceptions 

 which, indeed, constitute an essential part of his own 

 theory of heredity have stood the test of time in an 

 admirable manner. 



Let us turn our attention, then, for a short space to 

 the Germ-Plasm Theory of inheritance. -On Weis- 

 mann's theory, as in most other theories of heredity 

 from the time of Darwin and Nageli downwards, the 

 separate parts of the living organism are supposed to 

 be represented by separate material particles in the 

 germ-cells. These representative particles are known 

 as determinants. A complete set of determinants in 

 which every part of the organism is thus represented 



