SPERM ATOGENESIS OF APHIDS. 353 



other smaller chromosomes. This must be the reason why we 

 see four smaller chromosomes in the larger secondary spermato- 

 cyte instead of five. 



The side view of the metaphase of the smaller spermatocyte 

 differs from that of the larger one in shape. It is more spindle- 

 shaped (Fig. 22). Fibers are not seen distinctly in the prepara- 

 tions stained with iron hematoxylin. The two stained bodies on 

 both sides of the chromosomes in the equatorial plate might be 

 the centrosomes (Fig. 23). There are cases which show sep- 

 arated chromosomes, and cases which show massed chromosomes 

 (Figs. 23-25). So far as my observation goes, in most cases the 

 chromosomes seem to fuse soon after their splitting. The telo- 

 phase does not show distinctly the interzonal fibers as in the case 

 of the larger cell. Two equal smaller spermatids are produced 

 after the division. 



4. Smaller Spermatid. 



The germ cells of each cyst of the testes are generally in about 

 the same stage. When the spermatids are young the cysts are 

 spherical in shape, but they elongate during the development of 

 the spermatids. The young smaller spermatids (Fig. 28) have 

 condensed nuclei, but the larger spermatids (Fig. 18) between 

 which they lie have vesicular nuclei. These smaller and larger 

 spermatids are seen all through the cyst. I have examined many 

 cases in order to see whether the polarities of the larger and 

 smaller spermatids are established with relation to the epithelium 

 or not. Most of the young larger and smaller spermatids, which 

 are seen near the epithelium, develop their tails toward the center 

 of the cyst, but some of them may develop along the epithelium 

 or develop their tails toward the epithelium. Those in the cen- 

 tral part do not show any definite orientation, and in extreme 

 cases spermatids existing side by side may show opposite direc- 

 tions. In cysts in which the larger spermatids are developed to 

 the stage shown in Fig. 18, the orientation of the larger and 

 smaller spermatids remains unchanged. In a little later stage, 

 however, all the larger and smaller spermatids begin to orient in 

 the same direction, and when the larger spermatids develop to 

 the stage shown in Fig. 19, all are oriented in the same direction. 



