Japanese Tricladida Maricola. 29' 



ventral side of the body between the successive gut diverticulae, 

 presenting a somewhat metameric appearance. 



The testes are usuall.y ovoid or round in form, but sometimes 

 polygonal or lobate, as the case may be, they being subjected to 

 more or less pressure against one another. The fully grown testes 

 are in every way like the typical follicles of the Triclads. In St.- 

 trigo7iocephala they are comparatively small. Each testis is bound- 

 ed direct!}^ by a thin layer, the tunica propria, which assumes the 

 character of fibrous tissue, and is beyond doubt to be differentiat- 

 ed from the parenchyma, as mentioned by Böhmig. In the first 

 stage of development the testes appear as spherical clusters of cells, 

 which by division increase in number and arrange themselves in 

 the form of the follicles, normally packed full of sperm-mother- 

 cells and spermatozoa in all stages of development. Numerous, 

 cells, each containing a large nucleus, are arranged in a single 

 layer on the wall of the testis; they are loosely opposed to the 

 parenchyma. 



Vas Deferens. — The wall of the capsular testis gives rise to the 

 epithelium of the fine duct, by which the spermatozoa reach the 

 vas deferens. Generally two types may be distinguished in the 

 mode of communication of the testes with the vasa deferentia, 

 according to the position and arrangement of tlie testes. In the 

 first tj'pe, the testes communicate almost directly with the vasa 

 deferentia; while in the second type, they open into the latter by 

 means of fine testicular canals. 



In Pr. lactea each testis, occupying a dorsal position in the 

 body, gives rise, on its lower side, to a fine testicular canal or vas 

 efïerens. The Vasa efferentia proceed between the gut branches, 

 frequentl}^ uniting together to form somewhat wider ducts, and 

 then take a course directed towards either of the vasa deferentia. 

 They are more or less distinctly visible only when filled up with 

 spermatozoa. In St. trigonocephala and Ect. llmull. from each 

 testis lying ventrally arises a short vas efferens wdiich soon unites 

 with its fellow of the opposite« side to foi-m vasa deferentia. 



The vasa deferentia proceed backwards in Pr. lactea and St. 

 trigonocephala, along the inner side of the longitudinal nerve- 



