104 The Spermatogenesis of Desmognathus Fusca 



period of growth to form the spermatocytes. Mature and dividing sper- 

 matocytes occur sporadically, but seem to be those left over from the 

 preceding summer. During the winter a sluggish division of the 

 spermatogonia is taking place and a few lobules containing spermatozoa 

 or spermatids are usually encountered. There does not seem to be much 

 activity in the organ during the cold months, and there is practically 

 no increase in size, but in the spring mitoses become numerous and 

 more cysts of spermatogonia are found in stages of cell division. 

 Growth to form the spermatocytes also begins anew, continuing well 

 into July. During June and July, especially in July, divisions of the 

 spermatocyte are taking place, and multiplication of the spermatogonia 

 has practically ceased. The transformation of the spermatogonia into 

 spermatocytes stops in June, while the transformation of spermatids 

 into spermatozoa, beginning in June or July, extends through August 

 into September. Most of the spermatozoa leave the testis in the early 

 fall and the cycle begins again. 



The spermatogenetic cycle of Desmognathus corresponds closely, there- 

 fore, with that of Salamandra, differing in the extrusion of the mass 

 of the spermatozoa in the fall, so that the cycle may be said to begin 

 then instead of in the spring, though there is no great activity until 

 spring. The months when the processes of spermatogenesis are actively 

 taking place are the spring and summer months. During April, May 

 and June transformation of the spermatogonia into spermatocytes is 

 predominant; the divisions of the spermatocyte characterize July, and 

 the transformation of the spermatid, August. The processes, however, 

 overlap widely with doubtless considerable seasonal and individual 

 variation. 



The Testis. 



' This organ is quite elongated and attached to the dorsal wall of the 

 abdominal cavity by a mesorchium in which are the vasa efferentia, 

 blood-vessels, etc., as in other Amphibia. It is highly pigmented, as is 

 also the spermatic duct, the pigmentation diminishing with the expan- 

 sion of the organ as spermatogenesis proceeds. 



The structure of the Amphibian testis has been investigated by several 

 writers, among them von Wittich, Leydig, Bidder, Spengel, La Valette 

 St. George, 76, and Hoffmann, 78, all of whose papers appeared prior to 

 1880. Of these the papers of Spengel and Hoffmann appear most 

 valuable. Spengel, in his analysis of the structure of the organ, recog- 

 nized " capsules " (containing sperm-producing cells), connected with a 

 collecting duct by branch-tubules. According to the relations and ar- 



