TURBELLARIA. 



215 



or vice versa. This is probably only a case of successive hermaphro- 

 ditism common amongst the Turlellaria, a condition in which the 

 male organs attain maturity before the female. 



The generative organs are always complex, and the gonads are 

 either compact, or follicular and scattered. As a type of the first 

 condition we may .take Mesostomum Ehrenbergii (Fig. 170). Here 

 there is a single external opening leading into an atrium genitale, 

 into which opens the vas deferens (Vd) through the penis (P), the 



FIG. 170. Generative apparatus of Meso- 

 stomum Ehrenbergii (combined from Graff 

 and Schneider). S pharynx ; Go sexual 

 opening ; Ov ovary ; Ut uterus with winter 

 eggs; Do yolk -gland; Dg duct of yolk- 

 gland : T testes ; Vd vas deferens ; P 

 penis ; Rs receptaculum seminis. 



FIG. 171. Generative organs of 

 Vortex viridis (after M. Schultze). 

 T testes; Vd vas deferens; Vs 

 vesicula seminalis ; P penis ; Or 

 ovary ; Va vagina ; M uterus ; 1) 

 yolk-gland ; Rs receptaculum 



oviduct, the two uteruses (Ut), the receptaculum seminis (Rs\ and 

 the ducts of the yolk-glands (Dg). The testes (T) are paired and 

 tubular, their ducts join in the penis, which projects into the atrium. 

 The ovary (Ov) is single, and its duct opens directly into the atrium 

 yenitale. The receptaculum seminis stores up the sperm received in 

 copulation, and the eggs remain in the uterus for a shorter or longer 

 time. As a type of the second condition we may take the fresh-water 

 Triclad Planaria lactea. Here (Fig. 172) also there is a single external 

 opening (Go) leading into an atrium genitale, into which open the 



