B. F. Kingsbury 109 



and a more detailed discussion of the structure of the Amphibian testis, 

 the writer hopes to consider at some future time. 



The Geowth and Division or the Spermatocyte. 



As is well known, from the spermatogonia are formed, by a process 

 of growth, the spermatocytes of the first order. Eoughly speaking, 

 this transformation involves an increase in the size of the nucleus and 

 the amount of cytoplasm, together with chromatic changes resulting 

 in the formation of twelve chromosomes. The character, however, is 

 given to the cell at the beginning of the period of growth, so that in this 

 article the name of spermatocyte will be applied to it during this time of 

 development, a distinction being made when necessary by applying to 

 it the qualifying word " immature." The growth is evidently slow and 

 takes some time for completion. In the fall and early winter the 

 number of nearly mature spermatocytes is small. The mass of sper- 

 matozoa formed from the spermatocytes of the preceding summer, as 

 has been said, have been largely expelled from the testis, though a few 

 lobules usually still retain them. A few lobules likewise may contain 

 spermatids and immature spermatozoa. During the fall, on the other 

 hand, the spermatogonia are undergoing evidently rapid division, so 

 that entire cysts are often found in stages of mitosis, and this process 

 continues at a much retarded rate through the winter, to become very 

 active again in the spring. The transformation of spermatogonia into 

 spermatocytes, beginning in the fall, continues up to about the middle 

 of the summer when it ceases. Divisions of the spermatocyte of the 

 first order are but rarely found during the fall, winter and early spring, 

 though occurring sporadically, especially in the early winter. But dur- 

 ing late spring and early summer the divisions are abundant, continuing 

 up to August (about), when they have nearly ceased. 



A secondary spermatogonium of the last generation, small sperma- 

 togonium of Meves, 96, possesses a round or slightly oval nucleus of' 

 medium size. The chromatin is in the form of an apparent network 

 of irregular shape and distribution. One or two small nucleoli are 

 present. The amount of cytoplasm is small and is especially accumu- 

 lated on one side surrounding the idiozome (to use the name introduced 

 by Meves). Within the idiozome two centrosomes may usually be 

 distinguished. 



In the transformation into the spermatocyte, the network of chromatin 

 becomes changed into a thread which is, I believe, at this time already 

 segmented into the twelve chromosomes which are easily distinguishable 

 a little later in their growth. The spirems are at first very fine and 



