The spermatogenesis of Peripatus (Peripatopsis) balfouri. 287 



In the lumen of the slender vas deferens are found long coils of 

 interlacing spermatozoa in various stages of formation. No sperma- 

 tophores were found in those proximal portions of the vasa examined 

 by me. 



III. The Spermatogonia and their Mitoses. 



1. The Rest Stage. 



The spermatogonia are cells polygonal in outline by reason of 

 mutual contact, which form an ill-defined layer of from two to four 

 or five cells in depth on the periphery of the testis, this layer bounded 

 externally by the sheath of the testis (Fig. 1, Plate 19; Fig. 250, 

 Plate 24, Spg). The spermatogonia of the same testis vary in size, 

 and the smallest are found most peripherally. The nucleus (Figs. 1, 

 2, Plate 19; Fig. 233, Plate 23) is relatively enormous with regard 

 to the amount of the cytoplasm, elongated in the smaller cells, rounded 

 in the larger. The smallest cells are not found in every transverse 

 plane of the testis, but appear to occur in isolated patches; between 

 smallest and largest cells occur all intermediate stages ; the nuclei of 

 the smallest cells stain most deeply owing to the dense arrangement 

 of the chromatin in them. The chromatin is occasionally arranged 

 in the form of an apparently continuous reticulum (Fig. 2), but more 

 frequently the arrangement is looser, scattered chromatin granules 

 connected by linin fibres (Fig. 1). The nucleoli (w) stand generally 

 in close contact with the chromatin reticulum, and seldom lie each in 

 a clear zone; sometimes they are vacuolated. Usually they are nearly 

 spherical in outline ; but in numerous spermatogonia of one testis they 

 were extremely irregular in form (Fig. 2), — angular, lobular, elongated 

 and constricted: may these irregularities in form in different testes 

 be referred to the different states of nutrition of different individuals? 

 This conclusion has been made by Woltereck (1898) in a study of 

 egg cells of Ostracods, and it might possibly apply also to Peripatus. 

 The number of the nucleoli is quite variable, as the following count 

 shows, made on resting spermatogonic nuclei from two testes ; 38 nuclei 

 contained each 1 nucleolus; 115 nuclei contained each 2 nucleoli; 

 121 nuclei contained each 3 nucleoH; 73 nuclei contained each 4 

 nucleoli ; 42 nuclei contained each 5 nucleoli ; 17 nuclei contained 

 each 6 nucleoli; 7 nuclei contained each 7 nucleoli; 3 nuclei contained 

 each 8 nucleoli; 1 nucleus contained 9 nucleoli; and one contained 



