68 McCLUNG. 



vesicle is formed, the chromatic substance is deposited upon its 

 wall in intimate relation with the cytoplasm, a concentration 

 ensues and a definite chromosome is produced. 



These changes, it seems to me, are easily explainable if we 

 regard the conditions under which the processes operate. The 

 divisions of the spermatogonia are rapid and continuous and 

 every factor concerned is subordinated to filling the follicles with 

 spermatogonia as quickly as possible. This, of course, requires 

 a rapid increase in amount of chromatin including that of the 

 accessory chromosome, and so the anabolic processes are facil- 

 itated by bringing the chromatin into a position where it can best 

 derive its nourishment from the cytoplasm. The vesiculation of 

 the accessory chromosome is merely an incident, the isolation of 

 the element being the end sought. 



Throughout the divisions of the secondary spermatogonia this 

 process continues until the accessory chromosome of, let us say, 

 the primary spermatogonium has been apportioned to each of 

 the many cells that are now ready to transform into spermato- 

 cytes, and during this time it has practically been as independent 

 as if it were the chromatin of a separate nucleus. 



PART II. THEORETICAL CONSIDERATIONS. 



In seeking an explanation for the unusual phenomena con- 

 nected with the history of the accessory chromosome in the male 

 germ cells, it is most natural to surmise the existence of a phylo- 

 genetic significance. In the spermatagonia what amounts to 

 practically two nuclei in each cell is strongly suggestive, in mere 

 general features, of the appearances manifested in the Protozoa 

 where both macro- and micronuclei are present. The accessory 

 chromosome might be homologized with the micronucleus which 

 serves as a medium of exchange between the organisms during 

 the act of fertilization, but it would be extremely difficult to 

 trace any parallelism between the macronucleus and the real 

 chromosomic vesicle of the spermatogonia. I do not, therefore, 

 believe that we can look in this direction for an explanation of 

 the peculiar character exhibited by the accessory chromosome. 



Nor do I believe that there is the least basis for Paulmier's 

 theory that the structure is a degenerating chromosome. There 



