28 ARKIV FÖR ZOOLOGI. BAND M. N:0 13. 



feature of Chromoplaiia, certainly indicating a more advanced 

 stuge, is not a direct obstacle to my interpretation above, 

 but it may easily be interpreted as a secondarily acquired 

 condition, independent of relationship. It is certainly a 

 fairly general tendency in the Cotylea, where in the Eury- 

 leptidean series this approach of the male porus to the mouth 

 ciilminates in Stylostomum. But in the polyclads there is a 

 considerable variation of the distance between the male porus 

 and the mouth even in closely allied genera. One of the best 

 examples may be taken from the very natural acotylean 

 family StylocJiidoe, in the scope I have given it (Bock, 1913). 

 In the typical case the sexual pores are very close to one 

 another in the back end of the body (in Siylochus); in Idio- 

 planoides (= Woodivorthia Laidlaw, 1904) they are close to 

 one another but not removed so extremely near the posterior 

 margin of the body as in certain species of Siylochus; in 

 Gryptophallus and Farastylochus there is a fair distance be- 

 tween the sexual pores, and finally, this distance is consider- 

 able in Meixneria. In this family we may trace a back- 

 ward movement of the genital openings, while in the Eury- 

 leptidce a movement in just the opposite direction has taken 

 place. 



With regard to the female organs the ovaries are already 

 treated above. No uteri were observed in the specimens of 

 this genus, just as was the case in Chromoplana. That is 

 rather surprising, as the specimen of which the female appa- 

 ratus is drawn in Plate I, f ig. 5 possessed eggs nearly ready 

 for deposit, to judge at least from their appearance and 

 large size. It may, however, be pointed out that the nuclei 

 of the large oocytes have not yet entered into division but 

 that stage is never reached by the oocytes of other polyclads 

 while the eggs remain in the ovaries. Therefore one cannot 

 expect to find these oocytes either in such a stage. I am in 

 favour of the assumption that the uteri are never developed 

 in this polyclad rather than that they only appear låter 

 on in the individual life. Just the small number of eggs 

 delivered at the same time would render unnecessary an 

 assemblage sac, which the nterus of other polyclads in reality 

 represents. That a reduction of the uteri has taken place 

 in polyclads with a small number of ovaries is also to be 

 gathered from Enterogonhnus Hallez, Laidlaivia Herzig, 



