On the reproductive system of Planavia simplissima. 451 



found the connection in cases that seemed hopeless or established 

 such a complicated arrangement as that shown on PI. 32, Fig. 13, by 

 following the fine tubules cut at a slight angle for many sections. 

 More than this the outlet was found in the earliest stages examined 

 (PI. 31, Fig. 2 ie 1 and te 3). There seems therefore no reason to 

 doubt that it is well established and exists from the first. This, in 

 so far as it shows the testicular canal to be constant, is in line with 

 the condition described by Chichkopp ('92, p. 522), where the walls 

 of the testes collapse after they have finished their season of pro- 

 ductiveness and the follicle is reformed later by the division of the 

 few sperm-mother cells which remain between its epithelial walls. 



When it is seen that the elongated canals are interchangeable 

 with wider openings {Fl. montana and Fl. lactea Chichkoff, '92) a 

 question regarding the identity of the epithelium of the testes with 

 the lining of the finer canals and vasa deferentia can hardly be raised. 

 That the tubules connecting one follicle with another in Flanaria simplis- 

 sima are of germinal epithelium is evident from the fact that the shorter 

 ones often show small cavities with sperm-mother nuclei in the walls 

 (PI. 31, Fig. 2 tc and tc'). Similar connections of a greater length cannot 

 be considered of a different nature (PI. 32, Fig. 13 tc). The germ 

 cells make an epithehal lining for that part of every follicle where 

 they are not actually dividing (PI. 31, Fig. 2, and PL 32, Fig. 10) 

 and this germinal epithelium passes into the testicular canals in ex- 

 actly the same way as into the tubules connecting one follicle with 

 another which have been shown to be germinal. If the epithelium of 

 the vasa deferentia is equivalent to the epithelium of the finer canals 

 and to that lining the testes, the seminal vesicles are to be regarded 

 in the same light when it is found that their lining is identical with 

 that of the vasa deferentia and continuous with the epithelium of the 

 canals from the posterior testes (PI. 31, Fig. 8 te 5). 



The position and extent of the vasa deferentia is shown in 

 the general figures as vd. They lie just outside and above the 

 main nerve trunks on the ventral side and extend forward as pro- 

 longations of the seminal vesicles terminating in the testicular canal 

 of the most anterior follicle of either side. There is a well defined 

 lumen along the entire length, although its diameter varies even in 

 the same worm as does the size of the duct (PL 31, Figs. 5 and 6 vd) 

 and may even present enlargements in the nature of secondary seminal 

 vesicles filled with spermatozoa (PL 31, Fig. 1 en). During the period 

 in which specimens were examined the lumen was always present and 



