72 W. W. SWINGLE. 



The oogonial number of chromosomes in the female larvae 

 appears to be twenty-six. It was possible to make, however, 

 only a few counts, and this number stands, therefore, subject to 

 revision. The male spermatogonial counts will be discussed 

 later. Two oogonial counts were made from a specimen of 

 Rana catesbiana, which also gave twenty-six chromosomes as 

 the diploid number. (See Fig. i.) The size and shape of the 

 chromosomes in the two species of frog appear very similar. 



In the post-synizesis stages of the germ cells of the female 

 larvae of Rana pipiens, the chromatin threads which appear from 

 the dense, tangled, heavily staining contraction figure (Figs. 2 

 and 3), are thick, beaded structures, which have a marked tend- 

 ency to arrange themselves into the well-known bouquet figures. 

 At this stage all of the chromatin has become arranged in the 

 form of pachytene threads, except a rather large, heavily staining 

 body usually found adhering closely to the nuclear wall (Figs. 

 4-6). This body is somewhat irregular in shape, though constant 

 in size; the shape usually assumed is that of a triangle, with a 

 minute, thread-like structure at the apex. In the bouquet 

 figures, this chromatin mass orients itself toward one pole of the 

 cell along with the free ends of the pachytene threads (Fig. 6). 



Study of a somewhat similar body in the adult male indicates 

 that the body observed in the germ cells of the female larvae rep- 

 resents probably the accessory chromosomes. At the stage shown 

 in Figs. 4 and 6, the body appears double in most cells. In other 

 cells, for instance Fig. 5, the body is shown as single. Attempts 

 to trace this structure back through the synizesis stage proved 

 futile in my Rana pipiens material, owing to certain stains em- 

 ployed by me in connection with a different problem, but in 

 specimens of Rana catesbiana larvae 70 mm. in length, pre-syni- 

 zesis stages reveal a structure apparently identical with the 

 post-synizesis X-body of Rana pipiens. 



In female Rana pipiens, soon after the synaptic stages of the 

 maturation process occur, the young oocytes are formed and 

 further study of the .Y-body is impossible in the larval form. 

 Attention was then turned to the germ glands of young male 

 frogs. 



Through the kindness of Dr. B. M. Allen, I obtained a number 



