126 JESSE LE ROY CONEL 



not sufficiently advanced in development to indicate whether 

 they will eventually be male or female. 



Male. Myxine no. 15, an animal 62 cm. long, has a testis 

 band 5 mm, wide along the distal margin of the posterior 9.5 

 cm. of the mesorchium. Anterior to this band the mesorchium 

 is of comparatively uniform width (about 7 mm.) all the way to 

 the anterior end, and contains along its distal margin numerous 

 brown bodies (degenerated eggs) but no normal eggs. No brown 

 bodies, however, are present in the portion of the mesorchium 

 which is occupied by the testis band. The mesorchium is not 

 folded, but is straight and flat (fig. 82). There are no indications 

 that this animal ever produced large eggs, and it is considered 

 as an almost mature male. Only about one-half of the folUcles 

 contain cells which show mitotic figm-es, but no spermatozoa 

 were found. A transverse section of the testis band (fig. 77) 

 shows that, in this specimen, the large follicles are larger than 

 the largest ones in specimens no. 18 and no. 7, but they range in 

 size from small to large and are closely crowded together, so 

 that the stroma cells are limited to narrow strips between the 

 follicles or between the latter and the mesorchial sheath. Al- 

 most every stage of mitosis is represented. Not all the cells of 

 an individual follicle show mitotic figures, but what figures are 

 present are approximately in the same stage (fig. 78). 



A striking difference between the testis band of Myxine no. 

 15 and those of specimens no. 18 and no. 7 is the fact that the 

 single layer of squamous mesorchial epithelium which envelopes 

 the entire band has been here and there converted into a columnar 

 epithelium. The long, spindle-shaped cells of the mesorchial 

 sheath become shortened and arranged in palisade order. These 

 columnar cells have not entirely surrounded the testis band, but 

 in places the squamous epithelium is still present and forms the 

 sheath of the band. 



In two other specimens, no. 12 and no. 13, this process of con- 

 version of the mesorchial sheath into columnar epithelium has 

 advanced until the entire testis band is enveloped by it. The 

 band in these two animals is very different from that of any 

 other specimen. In the first place, the band extends the entire 



