2IO C. M. CHILD. 



VIII. The Full-Gr&wn Testis. 



The testis continues to increase in size for a considerable time 

 after spermatogenesis begins. Only a part of the spermatogonia 

 enter the spireme stage at any one time, the others continuing to 

 divide amitotically. After the appearance of the spermatogenetic 

 divisions in a testis, I have never seen a case of mitosis in the 

 spermatogonia, but amitoses are frequent. Figs. 62, A, 62, B 

 (PI. XVI.) represent groups of spermatogonia in full grown testes. 

 In the same testes all stages of spermatogenesis and fully devel- 

 oped spermatozoa may be found. At this period the spermato- 

 gonia are usually found in small groups near the periphery. 

 Figs. 63, A 63, D(P\. XVI.), show cases of amitosis in spermato- 

 gonia from full grown testes, including nearly all the modifica- 

 tions of the process observed. 



In Fig. 64 (PL XVI.), one half of a full-grown testis is shown 

 on a scale half as large as that of the other figures. The different 

 stages shown are as follows : at a is a group of spermatogonia 

 still in the prespireme stage and showing one amitosis ; b shows 

 the earliest stages of the spireme, c, c, two groups with fully- 

 developed spireme, while at d some cells are preparing for the 

 first spermatocytic mitosis ; at c is a cell in which the dyads are 

 formed, part of a group which appears in adjoining sections ; 

 f,f, are cytophores with spermatid nuclei and developing sper- 

 matozoa ; g, is a cytophore in which degeneration of the nuclei 

 has begun, but the spermatozoa are still attached ; at Ji is seen 

 part of a bundle of free spermatozoa which can be followed in 

 other sections ; k, k, represent two degenerating cytophores in 

 which the nuclei have already vanished : the shreds of cytoplasm 

 and the debris from earlier cytophores are indicated at /. Al- 

 though this one section does not show all the stages in the his- 

 tory of the cells, it serves to indicate the promiscuous distribu- 

 tion of different stages. 



IX. Conclusion. 



The point of chief importance in the present paper is the fact 

 that typical mitosis and amitosis may appear together and ap- 

 parently under identical conditions in the development of the male 

 as well as of the female germ cells. The relative frequency of 



