THE ACCESSORY CHROMOSOME. 63 



according to the usual laws governing cellular activities is seen 

 to be in strict accord with them. The variation from normal 

 conditions is, accordingly, manifested by those chromosomes 

 which emerge from the spireme of the first spermatocyte instead 

 of by the one which fails to enter into it. 



At the completion of the second spermatocyte mitosis the ap- 

 portionment of the chromatin to the germinal elements is accom- 

 plished and the further changes in the spermatid would seem to 

 indicate that there is no longer the necessity for the chromosomes 

 to maintain their separate identities. This, because the chromatin 

 first becomes diffuse and later condensed so as to form the head 

 of the spermatozoon where there is no distinction of parts. In 

 the spermatid where the accessory chromosome is present, there 

 is no apparent difference in the behavior of the nuclear elements. 

 The accessory chromosome runs the course of the ordinary 

 chromosome and sooner or later becomes indistinguishable in the 

 homogeneous mass of the spermatozoon head. 



It is, therefore, impossible to trace the location of the accessory 

 chromosome to any portion of this nuclear mass. The fact is 

 apparent enough, however, that it does remain a part of the 

 nuclear contribution to the mature element (^[ 12, 13, 23, 37, 

 43) and does not go to form a part of the archoplasmic deriva- 

 tions as Wilcox was at first inclined to believe (1| 23). The 

 merging of the chromatin elements into one mass makes it im- 

 possible to go further in the investigation of the accessory chro- 

 mosome at this point. We can hope to know more about it 

 only by learning its part in fertilization of the egg. As a result 

 of the action of the accessory chromosome in one maturation 

 mitosis, this fact, at any rate must be apparent, viz : that there 

 are two kinds of spermatozoa ; those ivith the accessory chromo- 

 some and those ivithout. Beyond this is speculation only, but 

 with accumulated observations on many forms it may not be long 

 until we are able to reach a definite conclusion regarding the ex- 

 act function of this well defined element. 



From the different observations, I hope (l) to bring out the 

 essential features which characterize the accessory chromosome, 

 (2) to show the extreme probability of its universal occurrence 

 among insects, (3) to outline its history in the different cell gen- 



