8 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



later cleavage nucleus of the egg. They are comparatively small vesicles 

 in which the chromosomes are closely aggregated and in which the 

 amount of linin is much smaller than in the "vesicle" stage. Thus 

 we see that during all the spermatocyte stages the cells exhibit phe- 

 nomena similar to those characteristic of the female germ cell under- 

 going maturation and cleavage. 



What is the explanation of this resemblance ? In my description of 

 the structure of the testis I have given in a general way the position of 

 the parts and the conditions surrounding the cells at various stages. I 

 will repeat this description here and see what conclusions can be drawn 

 from it. The testis is divided into a number of follicles, each one of 

 which is connected to the vas deferens by a tube which is continuous 

 with the wall of the follicle at one end (Fig. 1). The lumen of this duct 

 is continuous with that of the follicle, which extends nearly the entire 

 length of this structure and is filled with spermatozoa. Upon the ex- 

 treme periphery of each follicle are arranged the spermatogonia, either in 

 the resting stage or in various phases of mitosis. Next to these are 

 disposed in sequence from periphery to centre : (1) spermatocytes in 

 various stages of growth ; (2) first spermatocyte in the vesicle stage and 

 in various phases of the first maturation division ; (3) second spermato- 

 cytes in various stages; (4) spermatids; (5) young spermatozoa; and 

 (6), in the lumen, mature spermatozoa. 



These different cells in various stages are distributed in more or less 

 regular layers. There are, to be sure, many irregularities in this distri- 

 bution, the most pronounced appearing in follicles which are far advanced 

 in development. Here the closely packed spermatozoa fill the lumen 

 and show a tendency near the middle of the follicle to encroach upon the 

 younger cells, so that these are frequently forced aside, and the mass of 

 spermatozoa thus comes more or less close to the follicular sheath 

 (Fit, r . 1). However, the most typical arrangement is that which I have 

 mentioned. This is especially marked for the larger type of spermato- 

 cytes, which, as I shall show later, are always arranged in a definite 

 manner in the follicle. 



In the interstices between the cells, there is present at all stages a 

 substance of a more or less viscid consistency, which very probably serves 

 as nourishment. In testes which have been fixed this material consists 

 of a basis which in general structure very much resembles cytoplasm. 

 This reticular substance is not, however, of the same nature as cytoplasm, 

 its reaction to various stains being different. It does not show a strong 

 affinity for iron-haematoxylin nor for other similar stains, but is colored 



