282 RECENT CYTOLOGY 



determinant only, and not by both. Thus, not 

 only are all immediate ancestors not represented 

 in the germ - cells in respect of any particular 

 character, but only one of the parents is so repre- 

 sented to the complete exclusion, so far as we can 

 tell, of the other parent. In fact, we are led to 

 believe that the germ-cells contain one set of de- 

 terminants only a single id whilst the somatic cells 

 contain two ids only. The Mendelian theory is thus 

 seen to be considerably simpler than the germ-plasm 

 theory, which it replaces. At the same time it must 

 not be forgotten that many of the conceptions used in 

 the Mendelian expression of the facts are borrowed 

 from Weismann's theory, and that but for Weismann's 

 work it would have been impossible for us to have 

 got so far in the co-ordination of the facts derived 

 from experiment and microscopic observation re- 

 spectively. 



The preceding sketch may serve to show how Mendel's 

 observations have been found to throw light upon many 

 of the facts of cytology the meaning of which was pre- 

 viously obscure; and how it affords at the same time 

 a criterion by which may be tested the truth of theories 

 based upon the interpretation of minute phenomena 

 only made visible by the highest powers of the micro- 

 scope. The disinterment of Mendel's discovery took 

 place in 1900; and the rapid manner in which the 

 facts of cytology have been found to fall into line with 

 Mendelian conceptions augurs well for the future 

 progress of discovery in these fields. 



