74 McCLUNG. 



ova to spermatozoa. It would therefore be a necessary con- 

 tent of the cells until they had passed through the stages of de- 

 velopment beyond that at which they might pause and become 

 laden with yolk or, in other ways, postpone the period of matura- 

 tion. It is conceivable that the production of four functional 

 cells from one spermatogonium would call for the employment 

 of more energy than would the formation of one functional egg 

 from an oogonium, especially since many cells contribute their 

 substance or support in the upbuilding of the egg. 



Accordingly, it would be most reasonable to expect the pres- 

 ence of the determinant in the latest possible stage consistent 

 with its equal distribution to half the spermatozoa. This we find 

 to be the case with the accessory chromosome which regularly 

 occurs in all the cell generations up to the last and is only with- 

 held, finally, from half of the spermatids. By its consistent 

 course in this respect, the accessory chromosome plainly mani- 

 fests its intimate influence upon the germ cells of which it is a 

 part, and most strongly suggests a relation to sex determina- 

 tion. It may further be pointed out in reference to this relation, 

 that during the multiplied spermatogonial divisions, the accessory 

 chromosome exhibits a somewhat distant attitude toward the 

 remainder of the chromatin, and it is only at the time of the 

 definitive spermatocyte divisions that it comes to be an intimate 

 member of the cell nucleus. In what manner it is borne from 

 the fertilized egg to the testis of the embryo we do not know, 

 and, lacking this knowledge, are placed at a considerable dis- 

 advantage for a proper appreciation of its real character. 



(r) A most significant fact, and one upon which almost all 

 investigators are united in opinion, is that the element is appor- 

 tioned to but one half of the spermatozoa. Assuming it to be 

 true that the chromatin is the important part of the cell in the 

 matter of heredity, then it follows that we have two kinds of sper- 

 matozoa that differ from each other in a vital matter. We 

 expect, therefore, to find in the offspring two sorts of individuals 

 in approximately equal numbers, under normal conditions, that 

 exhibit marked differences in structure. A careful consideration 

 will suggest that nothing but sexual characters thus divides the 

 members of a species into two well-defined groups, and we are 



