THE SPERMATOGENESIS OF A. DAPHNID. 135 



various stages of maturation, the cells of an island being in 

 about the same stage. 



As the cells in these' islands advance in development a ring of 

 undifferentiated cytoplasm* remains about each island. This 

 cytoplasm is continuous with that surrounding other islands and 

 also with the cytoplasm of the giant cells (Fig. 2), which lie 

 between the islands. 



> 



\ 



FIG. i. 



The islands remain distinct until their contents are transformed 

 into free spermatids. The cytoplasm between the islands then 

 disintegrates, producing large spaces in which lie the free sper- 

 matids. The testis thus acquires a lumen which ever increases 

 in size until the testis becomes a hollow sac full of ripe sperm. 



In the last stages, when the testis is a hollow sac whose walls 

 consist merely of an epithelial coat, the giant nuclei are not to 

 be found. However, there may be seen, scattered among the free 

 sperm, irregular particles of disintegrating cytoplasm, possibly 

 the remains of the rings of cytoplasm which formerly enclosed 

 the islands. 



