204 MENDELISM 



our ideas of heredity, since we no longer look upon 

 the individual as a unit, but find ourselves compelled 

 to study separately the independent characters of 

 which the individual is built up. The idea of the 

 individual as a living mosaic an idea put forward long 

 ago by Naudin with only a partial realization of its 

 significance has thus returned to us. In this con- 

 nection a curious problem presents itself. What 

 would be left if we could imagine all the separable 

 characters of a living creature as having been taken 

 away ? Would there, or would there not, be any 

 residuum ? Upon this knotty point there is a disagree- 

 ment among authorities, and so we may be content 

 to leave it, since the question is hardly one which is 

 capable of a practical solution. 



A phenomenon to which it is scarcely doubtful that 

 Mendelian principles will ultimately be found to apply, 

 although as yet the precise proof is wanting, is that of 

 sex. In the male and female sexes of the majority of 

 animals we have a very clear example of a pair of 

 definite differentiating characters. And the fact that 

 in the majority of forms the two sexes make their 

 appearance in nearly equal numbers, may be thought 

 to point clearly to the conclusion that the separation 

 of the sexes depends upon some quite simple gametic 

 process. Light has recently been thrown upon this 

 question from the side of the study of the minute 

 structure of the gametes, and we shall defer the further 

 discussion of the problem to the chapter which deals 

 with microscopic phenomena within the cell. 



A proper understanding of Mendel's law enables us 



