276 THE UNIVERSITY SCIENCE BULLETIN. 



since these were the only tissues that had been taken with the 

 testes from the body of the animal at the time of cytological 

 preservation. The carcass itself unfortunately was preserved 

 in a weak solution of formalin. The fact however, that "fat 

 body" cells and the cells of the testicular follicles and of the 

 vasa efferentia show fourteen chromosomes is reason for think- 

 ing that this number would likely have been found in all 

 somatic cells. 



In the germ cells (spermatogonia, figs. 6 and 7 ; first sperma- 

 tocytes, figs 8 to 21 ; and second spermatocytes, figs 22 to 27) 

 this chromosome is uniformly present. It is here that, on 

 account of the singular behavior of accessory chromosomes 

 normally exhibited in spermatogenesis stages, a clew is first 

 obtained as to the probable nature of this supernumerary body 

 which resembles in every way an accessory chromosome. Its 

 characteristics are as follows : 



(1) It may be recognized along with the accessory in syn- 

 apsis and growth stages by its condensed condition (figs. 8 to 

 16). 



(2) In "bouquet" of synapsis, intermediate finely threaded 

 or netlike, and early prophase stages of the first spermatocyte, 

 it always lies near the wall of the nucleus, which is character- 

 istic of the accessory chromosomes (figs. 8 to 13). 



(3) It condenses ahead of the other chromosomes in pro- 

 phases of the first spermatocyte (figs. 14 to 16). 



(4) It has a tendency to pair side to side with the accessory 

 during parasynapsis stages when other chromosomes are simi- 

 larly pairing (figs. 8 to 11) . This occurs in about from 65 per 

 cent to 75 per cent of cells. At this time both the accessory 

 and the supernumerary have the form of a right-handed 

 corkscrew like spiral (fig. 8). At later stages, they lie not so 

 closely together, though there is evidence, in many of the cells, 

 that they are in some way attached to each other (figs. 14 to 

 19). The synapsis seems to be most intimate at the pointed 

 ends, which, judging from the general position in the cell and 

 from the direction of orientation of the ordinary chromosomes, 

 I have a surmise may be the distal ends. Further evidence 

 of the association or pairing which occurs in synapsis is 

 afforded by their behavior in the first spermatocyte division 

 (figs. 17, 18, 19). In some cases (fig. 17) they are traveling 

 to the same pole closely approximated to each other ; in other 



