No. 4-J MALE REPRODUCTIVE CELLS OF INSECTS. 189 



mass is a half of the boomerang-shaped body which has been 

 divided longitudinally in the same manner as the ordinary 

 chromosomes. When this is observed projecting down from 

 the middle of the group of chromosomes, thus presenting its 

 broadest surface, it exhibits the form of an attenuated " U," the 

 curved end of which is in contact with that of its fellow on the 



Fig. 5. — Late anaphase of the spermato- 

 gonia exhibiting the accessory chromo- 

 somes divided and still attached at their 

 ends in the equatorial plate. 



Fig. 6. — The same viewed from the side. 



Other side (Fig. 5). In cases where the section is cut so that 

 the thread depends from the side of the group, the two chro- 

 matic masses present, roughly, the appearance of two hands 

 with the index fingers pointing toward each other (Fig. 6). 



In the resting stage of the spermatocyte that succeeds the 

 appearance just described, the accessory chromosome again 

 appears as it did in the resting stage of the spermatogonia, and 



Fig. 7. — Early prophase of the sperma- 

 tocyte. The accessory chromosome in 

 the form of a coiled thread. 



Fig. 8. — Later prophase of the sperma- 

 tocyte. The accessory chromosome 

 " U "-shaped. 



would easily be taken for an ordinary nucleolus. Soon, how- 

 ever, it commences to assume a threadlike form which finally 

 results in the production of a long " U "-shaped body, a form 

 that is retained during the greater part of the spireme stage 

 (Figs. 7-9). In this condition, it lies at the surface of the 

 vesicle and stains in its usual intense manner. Concurrently 

 with the formation of the " rings " from the spireme thread, it 



