CHROMOSOME COMPLEX OF SPERMATOCYTES. 



309 



exhibits a very unusual appearance, because of the heterogeneous 

 condition of its parts. Besides this structural difference, the 

 accessory chromosome is further made noteworthy by the fact 

 that it is shorter than the other thirds of the multiple element. 



When the mitotic figure of the first spermatocyte is formed 

 the hexad takes a position parallel to the axis of the spindle with 

 the division between the 

 parts of the original bi- 

 valent chromosome in the 

 equatorial plate. As it lies 

 thus it is almost as long as 

 the spindle, but has ap- 

 proximately two thirds of 

 its length on one side of 

 the equatorial plate. This 

 greater portion includes, of 

 course, the accessory chro- 

 mosome. Since the fibers 

 always attach to the ends 

 of the chromosomes, the 

 accessory becomes bent 

 away from the spindle and 

 lies at a more or less ob- 

 tuse angle to the rest of 

 the chromosome. The 

 mantle fiber then attaches 

 to the angle thus estab- 

 lished. A similar arrange- 



FlG. 3. Lateral view of the first sperma- 

 tocyte prophase with a number of thechromo- 

 somes drawn. The hexad is shown in profile 

 with the accessory chromosome, "a.f.," char- 

 acteristically bent back at an angle. These, 

 and all other drawings in this paper, were 

 made under a camera lucida and are repro- 

 duced here at a magnification of 1,900 diam- 

 eters. 



ment is mentioned by de 

 Sinety for the phasmid Leptynia. 



With the beginning of the anaphase this multiple chromosome 

 separates at the point where the two chromosomes were united 

 in the spermatogonia, so that to each end of the spindle there 

 goes one of the spermatogonial elements, but the accessory 

 chromosome, on the contrary, becomes a member of only one of 

 the daughter nuclei. Thus it happens that in the first sperma- 

 tocyte where the quantitative division of the other chromosomes 

 occurs this one element is divided qualitatively. In effect this is 



