SPERMATOGENESIS OF APHIDS. 355 



I 



have condensed ovoid nuclei which elongate later, the criterion 

 by which to distinguish them is their position, since when they 

 have developed to such a stage, the smaller spermatids with con- 

 densed spherical nuclei have already left the epithelium. 



The metaphase of the smaller secondary spermatocytes are 

 seen among those of the larger secondary ones; I think, there- 

 fore, there is no doubt that the smaller secondary spermatocytes 

 undergo the second division. More developed larger spermatids 

 are seen with more developed smaller spermatids in the same 

 cyst. We may conclude from these observations that the smaller 

 spermatids develop with the larger spermatids. 



I have observed cases where the larger and smaller sperma- 

 tids are seen in the central part of the cyst, while the majority of 

 spermatids have already reached the sustentacular cells. Such 

 larger and smaller spermatids might fail to reach the susten- 

 tacular cells, since they have to move among the spermatids. The 

 examination of the later stages, however, has shown that they 

 succeed in reaching the sustentacular cells. 



Figure 32 shows a smaller spermatid which is abnormally big 

 and has a distinct axial filament. Ordinarily the smaller sperma- 

 tids elongate similarly, but are more delicate. One of the most 

 developed smaller spermatids is shown in Fig. 33. In such a 

 stage their development comes to a standstill, and they begin to 

 retrogress. They gradually retreat toward the tails of the larger 

 spermatids. Their nuclei which are deeply stained with iron 

 hematoxylin are seen among the tails of the larger spermatids 

 in a somewhat regular position. Finally they pass out to the 

 cavity -of the cyst. 



The smaller spermatids fail in attaching to the sustentacular 

 cells ; they cannot, consequently, get material for their further 

 development. They have to live on their own substance. Their 

 tails become shorter, and the cytoplasm around the nucleus in- 

 creases (Fig. 34). 



The forms shown in Fig. 35 are seen near the tail of the fully de- 

 veloped functional spermatozoa in the cavity of the cyst. We do 

 not see such spermatids in the cavities of the cysts at the younger 

 stages. These smaller spermatids still have elongated tails, but 

 later transform into spherical cells which have a distinct cell 



