SIXTEN BOCK, TWO NEW COTYL. GEN. OF POLYCLADS. 11 



in this exposé be taken together as they are undoubtedly 

 closely akin. They contain the greatest number of cotylean 

 genera with the main part of the species. The body is more 

 or less ovate and usually with two marginal tentacles. The 

 tentacles may sometimes be reduced (Stylostomum) or löst {Ace- 

 ros), the tentacle eyes still indicating them and their place. 

 We see how the pharynx is still folded in the Pseudoceridce 

 hut in a less excessive degree and acquires a bell shape in 

 the Euryleptidce. The male copulatory apparatus has in 

 these two families a conformity nnknown elsewhere among 

 the turbellarians. That it may be double in some species 

 of the Pseudoceridce is of no great sjT^stematic importance, 

 the structure of the apparatuses being quite of the typical 

 aspect. The penis is always (when single) directed forward 

 and is armed with a stylet and provided with penis-folds. 

 The prostatic vesicle is independent and opens together with 

 the seminal vesicle situated usually posteriorly, at the base 

 of the penis. The female organs show variability in the 

 oviducts, uteri, accessory vesicles, but the median »copula- 

 tory» apparatus (the short vagina seems here to be used only 

 or chiefly for the deposit of the eggs, the sperma being as 

 a rule injected in the tissues of the body without regard to 

 the place) is exactly of the same, very simple type. An 

 interesting feature is that it is always provided with a trans- 

 verse dilated shell chamber. 



3. The Prosthiostomidce form the third of the cotylean 

 types known to Lang 1884. They have an elongated bodj^ 

 and lack tentacles. The pharynx is tubular and the mouth 

 is close behind the brain. The main gut is very long, pro- 

 vided with numerous non-anastomosing gut-branches. The 

 male apparatus is of a type unique in the turbellarians: a 

 short penis armed with a hook-like stylet and two strongly 

 musculated accessory vesicles; the granular glands are in the 

 penis fold. The seminal vesicle lies behind the penis. The 

 female median- apparatus conforms to the type previously 

 mentioned. 



It is obvious that when considering the systematic po- 

 sition of Chromoplana the first and third of these types 

 must be left out of account. With this second series, form- 

 ing the heavy centre of the cotyleans, there is agreement 

 in some respects but not sufficiently great to include the 



