DIFFERENTIATION, HEREDITY, SEX 295 



of arrangement of its dissimilar component granules. The 

 relation of the reducing division to the chromosome depends 

 upon the character of the synapsis, whether telosynapsis or 

 parasynapsis, and also upon the behavior of the chromatin 

 granules in all these events, and it is difficult to be certain of 

 this. It is safe to say, however, that in most cases each biva- 

 lent chromosome, composed in equal parts of substance from 

 each parent, clearly separates into four elements, two having 

 one composition, two another. These elements are then dis- 

 tributed to separate gametes, so that with respect to the com- 

 position of each separate chromosome, the gametes produced by 

 an organism are of two kinds, approximately equal numerically. 

 This accords perfectly with the facts of Mendelian heredity, 

 upon the supposition that there is a correspondence between 

 chromatic elements and organismal traits. This may be made 

 somewhat clearer with the aid of a diagram: see Fig. 80. 



In the process of maturation, therefore, it is easily possible 

 to find a mechanism which permits the segregation of charac- 

 teristics in the germ cells and their distribution to separate 

 organisms in regular Mendelian ratios. One important corre- 

 spondence should not be overlooked. In Mendelian heredity 

 the individual qualities of the parents may not appear sepa- 

 rately until the first generation after the hybrids. This is 

 possibly related to the fact that the parental chromosomes 

 undergo synapsis and subsequent redistribution first in the 

 germ cells formed by the hybrid, and the segregated elements 

 are, therefore, distributed separately first in the organisms 

 formed from these hybrids, i.e., in the F t generation. 



The conclusion resulting from the study of Mendelian hered- 

 ity, that the organism is a sum of "unit characters" which 

 in the organism interact with one another, so as to produce 

 a physiological whole, but which in heredity are more or less 

 clearly separable units, affords strong evidence for the general 

 hypothesis of the representative particle composition of the 

 germ nuclei. Chromosomes might thus represent groups of 

 such "units" or in occasional instances perhaps, single units, 

 although this must be the case only rarely, for the total number 



