9. THE RFPRODUCTIVE SYSTEM 



93 



consist of a rather spongy layer of large transparent cells (Fig. 45). Finally, 

 in the postannular region of the sperm sac this layer is hardly developed at all 

 and often only the ciliated bands remain. These consist of large well- 

 differentiated cells with long cilia (Fig. 46). 



The lumen of the sperm sac contains a fluid filled with floating masses of 

 male germ cells. The latter are found in all stages of spermatogenesis from 

 spermatogonia to ripe sperm and form characteristic morulae or packets 

 consisting of cells all at the same stage of development (Fig. 62). Amongst 



Fig. 62. Successive stages in spermatogenesis of Lamellisabella zachsi. A - 4-cell stage; В - sperma- 

 tocyte morula ; С - spermatid mass ; D - mass of sperm. 

 cph - cytophore. ( After Ivanov, 1958a.) 



them one sometimes comes across comparatively large rounded cells which 

 appear to be gonocytes. One of the succeeding stages is represented by con- 

 joined groups of four cells (Fig. 62/4). Their further multiplication produces 

 characteristic multicellular spermatospheres or morulae. Part of the proto- 

 plasm of the cells is extruded into the centre of the morula in one common 



