538 STANLEY C. BALL 



femininum and oviducts exist only potentially in the undiffer- 

 entiated mass posterior to the atrium. 



The shell glands develop below the antral mass before the 

 lumen of the latter appears. At this stage the testis has become 

 functional; one can easily distinguish spermatogonia at the 

 anterior end, the primary and secondarj^ spermatocytes, sper- 

 matids and mature spermatozoa. Many of the latter now appear 

 in the thick-walled seminal vesicle. The genital pore does not 

 open until later. 



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