Anatomy and Histology of Nemer tines. 399 



sheath — in tlic latter case at some distance from its exterior 

 aperture. Tlie same thins; very probably occurs in Genne- 

 mertes pahiensisj only in this case the opening of the alimentary 

 canal is carried right to the anterior extremity, so that, as a 

 matter of fact, the apertures of mouth and proboscis coincide. 

 In Malacohdella, however, the proboscis-sheath oj)ens into a 

 peculiar cavity, which is provided with villi, and must be 

 regarded as a veritable jiharynx. Von Kennel ^ would have 

 us believe that the cavity of the proboscis-sheath 0]:)ens into 

 the mouth in Geonemertes palaensis also ; but it appeal's to 

 me, according to the figure which the author gives, that the 

 condition is precisely the same as in Monogonopora and 

 ProsadenoporuSj that is to say that the oesophagus opens into 

 the most anterior portion of the cavity of the proboscis-sheath. 

 The aniis, which is never absent, is always terminal. 



Von Graff t, too, asserts that the proboscis-sheath in Geo- 

 nemertes chalicophora opens into the mouth. But on referring 

 to Taf. xxvi. fig. 7, of the work in question, we see quite 

 clearly that the oeso])hagus opens into the proboscis-sheath at 

 a considerable distance from the external aperture of the 

 latter; it curves distinctly upioards, and the opening of the 

 proboscis — of the mouth according to von Graff — is almost 

 exactly terminal in this form, whereas it should be ventral if 

 it were the mouth-opening. In all respects the structure 

 presents the appearance of a prolongation of the proboscis- 

 sheath. 



In the intestine of the Nemertine we have the type of that 

 of the Annelid. If, however, we attempt a comparison with 

 the intestinal tract of a Turbellarian, even though we select 

 Gunda segmentata for the purpose — a form distinguished by 

 the possession of a straight unbranched intestine, which is 

 provided with a regular series of caecal evaginations and opens 

 into a mouth placed at the extreme anterior end of the body 

 — we nevertheless unavoidably fail ; for the intestine of our 

 Turbellarian, however far it may have diverged in develop- 

 ment from the radially-branched organ of the Polyclad, in the 

 direction of that of the Nemertine, is devoid of an anus. 



According to Hubrecht \ and Max Miiller § the proboscis 



* Von Kennel, "Beitrage zvir Kenntnis der Nemertinen," Arbeiten aus 

 dem Zool. Inst, zu Wiirzburg, Bd. iv. 1877. 



t Von Graff, "Geonemertes chalicophora, eine neue Land-nemertme," 

 Morphol. Jahrb. Bd. v. 1879. 



X Hubrecht, 'Report of the Scientific Results of the Voyage of 

 II.M.S. ' Challenger,' 1873-1870,' Zool. vol. xix. Nemertea, 1887. 



§ Max Miiller, * Obseryatioues Anatomicpe de Vermibus quibusdam 

 maritimis,' Berolini, 18.52. 



