6 ARKIV FÖR ZOOLOGI. BAND 8. N:0 25. 



furnished with a diverticulum pointing forwards; 1 in Dia- 

 phana the oesophagus was running straight backwards and 

 had no diverticulum. The walls of the oesophagus have 

 strong longitudinal folds, ciliated in Diaphana, cuticularized 

 in Ptisanula. In the last-named form the section of the oeso- 

 phagus is circular; further back it widens, the folds grow 

 more numerous and become a thicker cuticula, and, exteriorly, 

 a circular muscular layer. The stomach has a triangulär 

 section (Fig. 12) and its onter or left side is especially strongly 

 cuticularized; here also the basal part of the epithelium is 

 chitinoid and the cells of the stomach epithelium are flattened. 

 The triangulär section and the armed walls of the stomach 

 seem to indicate a primary stage of the conditions found in 

 other genera of Tectibranchia, where 3 chitinoid or calcareous 

 plates are situated in the walls. The stomach gradually passes 

 into the intestine, which is narrower and oval in section; it 

 is furnished with only a thin cuticula and a feeble muscular 

 layer. 



In Diaphana no cuticularization of the stomach walls 

 has taken place; the epithelium is like that of the oesophagus 

 and of the intestine, consisting of cylindrical ciliated cells ; 

 in the stomach, however, the cilia are fused to a basal mem- 

 brane. No muscular fibres surround the walls on the exteriör. 



In Ptisanula the stomach and the intestine were filled 

 with a roass of partly masticated matter, that had been 

 devoured. It consisted chiefly of small elongate cells appar- 

 ently arising from some animal food that had probably been 

 absorbed from the small hydroids among which the specimen 

 was living when it was taken. The stomach of Diaphana 

 was empty in both specimens, a circumstance indicating that 

 they may be carnivorous like Buccinum, Nassa and other 

 Gastropods, where the intestine is usually observed to be 

 devoid of food (Petersen 1911). 



The Genital Apparatus. On the right side of the 

 head of Ptisanula, just in front of the eye and somewhat 

 behind the mouth, a canal debouches under the head-lobe; 

 this appears to belong to the male genital apparatus. If the 

 canal is followed backwards, it will be found to lie above 

 and to the right of the pharynx and to stretch somewhat 



Cfr Newnesia in the anatomical account given by Eliot (1906). 



