348 The Vnitij of the Organism 



raised again, though in a quite different form. 



This demonstration of the existence of two kinds of sper- 

 matozoa and McClung's guess as to its meaning came at 

 an opportune time for their influence upon investigation. 

 On several accounts interest in cell structure was already 

 largely centered in the chromosomes. Furthermore, the 

 Mendelian mode of inheritance was rediscovered almost 

 simultaneously with the publication of McClung's hypothesis. 

 Now the most fundamental thing so far recognized in con- 

 nection with this sort of heredity seems to be separateness 

 and stability of the attributes of organisms ; the unit char- 

 acter concept, it has been usually called. As soon as the 

 natural suggestion was made that sex itself might be a unit 

 character, the alluring surmise was close at hand that attri- 

 butes of adult organisms which segregate in inheritance, that 

 is, which come out in pristine purity in the children, no 

 matter how much they may have been obscured in the par- 

 ents, might be connected with particular chromosomes. Add 

 to these circumstances the more general one that the estab- 

 lished facts and proposed hypotheses were congenial to the 

 elementalist spirit already powerful in biology, and the 

 tremendous impetus to work on the fascinating problems of 

 the mechanics and cause of heredity in so far as sexually 

 propagating organisms are concerned, can be easily under- 

 stood. 



It is doubtful whether in the whole history of biology 

 any other fifteen-year period has seen greater intensify of 

 investigation or a larger number of notable observations 

 and discussions on any topic than has the period since 1900 

 on the problem of heredity and sex. And "determinants", 

 (hypothetical somethings in the germ which "carry" and so 

 explain characters of the adult), modified into "determin- 

 ers" apparently for the purpose of disguising the unpala- 

 tableness of Weismannian metaphysics, have played a very 

 great part in the efforts that have been made. Indeed, there 



