THE SPERMATOGENESIS OF UMBRA LIMI. 121 



seasonal variation which influences, to some extent, the seasonal 

 cycle in the testis. During the summer of 1924, a comparatively 

 wet and cold season, testicular cysts which during a normal 

 season would show a great many maturation divisions had not 

 advanced any further than the formation of spermatogonia. 



SPERMATOGONIA. 



i. Origin. How is the new crop of germ-cells formed at the 

 beginning of each seasonal cycle? Are they produced from 

 reserve germ-cells which in turn are descended from other reserve 

 cells, or are they formed anew from migrating cells which come 

 from some point outside the lobule? Turner ('19), found the 

 latter to be true for the perch. Hargitt ('24), working on the 

 adult salamander (Diemyctyhis viridescens} , found that the 

 spermatogonia are formed anew each season from the epithelial 

 cells which line the collecting tubules or from the peritoneal 

 tissue which covers the testis. Although no effort has been made 

 by the writer to trace the origin of the early spermatogonia 

 outside the testis, there seems to be little doubt that in Umbra, 

 as in the perch, the primary germ-cells or early spermatogonia 

 arise anew each season from cells which migrate into the lobules 

 from some outside point. A certain amount of migration and 

 growth, indeed, seems to be in progress throughout the entire 

 cycle of spermatogenesis. Occasional small ameboid cells are 

 to be seen along the lobule wall or between the walls in small 

 numbers during August and early September when the testes 

 are filled with spermatogonia, spermatocytes or spermatids and 

 spermatozoa. In material collected from the first to the middle 

 of September, during which time most of the testis becomes 

 filled with spermatozoa, single large resting cells or clusters of 

 cells may be found scattered throughout the lobules. Whether 

 these degenerate or remain in a resting state with an occasional 

 division is not known. Clusters of large cells are found in 

 isolated cases still persisting in the fall but since no such cysts 

 are found the following spring, it is inferred that they have 

 given rise to spermatozoa during the winter. The large isolated 

 cells which may be found along with a few ameboid cells in 

 lobules which have completed their cycle of spermatogenesis may 



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