HA TAI. 



[VOL. I. 



somewhat polygonal, firmly connected, and possess compara- 

 tively small nuclei, (b) The cells of the central part are 

 larger than the former, becoming gradually spheroid and more 

 loosely connected ; the nuclei are larger, and the peritoneal 

 membrane of the testis disappears in this region, (r) At the 

 free ends of the testis the cells present completely spherical 

 forms, and are so loosely connected that they may be easily 

 detached. The spermatogonia have conspicuous nuclei. Each 

 fully matured spermatogonium has one large nucleus, and is not 



multinucleate, as in 

 Lumbricus (Calkins). 

 2. Spermatocytc 

 (Figs. 2, 3). - - The 

 primordial germ-cells, 



a 



FIG. 2. 





FIG. i. 



FIG 3. 



FIG. 4. 



or spermatogonia, when fully matured drop from the testis ; 

 sometimes one or two, but usually many at the same time, after- 

 wards swelling up gradually. When they are first detached 

 from the testis, no changes are noticeable, but with the begin- 

 ning of cell division the following nuclear changes are ob- 

 served : The nucleus of each cell in the outer layer moves 

 inward toward the center of the cluster, as shown in Fig. 2. 

 Each nuclear membrane disappears, while the chromosomes 

 become distributed evenly throughout the nucleus. Soon the 

 chromosomes collect in the equatorial plane (Fig. 3) and 

 undergo division by the usual method of karyokinesis (Fig. 4). 

 The spermatid arises after two or more such divisions. The 

 cells at the central part show no signs of change, but remain in 

 the resting stage. 



