66 bulletin: museum of comparative zoology. 



of connective-tissue cells, which are easily distinguished by their 

 relatively small size and deeply staining nuclei. These cells extend 

 proximally along the center of the follicle for some distance, forming a 

 more or less distinct longitudinal rachis. Proximal to the primary 

 spermatogonia are the secondary spermatogonia arranged in groups, 

 which are surrounded by a thin but distinct membrane, composed of 

 connective-tissue cells, each group constituting a spermatocyst. Each 

 spermatocyst remains distinct from its fellows from the time of its 

 formation until the spermatozoa become mature. The spermato- 

 cysts are arranged in regular sequence from the distal to the proximal 

 end of the follicle, so that successively older stages in the development 

 of the germ cells are encountered as one goes toward the proximal 

 end. This is, of course, due to the fact that existing cysts are con- 

 tinually being forced toward the vas deferens by the formation and 

 growth of new cysts at the distal end; thus cysts which are formed at 

 about the same time come to" occupy neighboring positions in the 

 follicles. 



Surrounding the whole is a distinct follicular wall, in which flattened, 

 deeply staining nuclei can be distinguished at intervals. 



In Steiroxys the structure of the testis is much the same, except that 

 in the later stages a single spermatocyst may come to occupy the entire 

 cross-section of a follicle. 



2. The Spermatogonia. 



A. Dissosteira Carolina. 



The primary spermatogonia (Plate 1, Fig. 5) are large rounded 

 cells situated at the distal end of the follicle. Each cell contains a 

 large eccentrically placed nucleus, which is usually more or less 

 irregular or lobulate in shape, the nuclear membrane often extending 

 out in the form of short sacculations, like the fingers of a glove. This 

 irregular or polymorphic form of the nucleus is more marked in the 

 secondary spermatogonia, where it will be considered more at length. 

 On one side of the primary spermatogonia the cytoplasm is much more 

 abundant than elsewhere, and adjacent to this cytoplasmic mass the 

 nucleus is flattened or concave. At the height of the resting stage 

 the chromatin is distributed through the nucleus in the form of fine 

 granules suspended in the linin network. At intervals, especially at 

 the intersections of the linin threads, the chromatin granules tend to 

 aggregate in irregular masses. In addition, the nucleus contains one, 



