ACCESSORY CHROMOSOME IN A FROG. 73 



of sections of the testes of young frogs killed several weeks after 

 metamorphosis had occurred. One of these young frogs was a 

 pseudo-hermaphrodite, over a year old. The testes of this ani- 

 mal contained both ripe spermatozoa and large oocytes. The 

 germ glands, though containing many oocytes, were true testes; 

 i. e., the animal was a modified male. All stages of the matura- 

 tion process were visible; in many follicles the oocytes and 

 ripe spermatozoa occurred side by side. 



The sections had been stained with haem-alum, counter stained 

 with eosin when received by me. This stain serves very well for 

 the maturation divisions, but is not to be recommended for 

 spermatogonial counts, as it renders the outlines of the chromo- 

 somes hazy. As a consequence of this, all of my spermato- 

 gonial counts were obtained from sections of testes from other 

 animals, stained with iron-alum haematoxylin. 



Ten or twelve spermatogonial counts gave twenty-five chromo- 

 somes as the diploid number. (See Figs. 7-9.) The chromo- 

 somes vary greatly in size and shape, from large V-shaped bodies 

 to small straight rods. 



In the hermaphrodite specimen a great many prophases of 

 the first spermatocyte division were found. The chromosomes at 

 this stage were undergoing reduction in number, and appeared 

 as thirteen ring and dumb-bell-shaped bodies of varying size. 

 (See Figs. 10-12.) At slightly later stages, the rings assume 

 the dumb-bell shape also, and are connected end to end by fine 

 linin threads. Still later stages show the linin connectives break- 

 ing and the chromosomes becoming scattered through the nucleus. 

 There are thirteen chromosomes visible in the cells. Near the 

 end of the early prophase period, twelve of the typical dumb- 

 bell-shaped prophase chromosomes round off somewhat, becoming 

 oval-shaped; one of the dumb-bell bodies, however, retains its 

 shape; this body, because of its peculiar behavior, I have termed 

 the X-body. It is not difficult to identify at this stage because 

 of its large size and dumb-bell shape (Fig. 13). 



During the early metaphase stages of the first spermatocyte 

 division, the prophase chromosomes, now oval-shaped, except 

 the .Y-body, line up in the equatorial region of the cell to form 

 the metaphase plate. The X chromosome takes its position on 



