Anatomy and Histology of Nemertines. 399 



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

 aperture. The same thing verj probablj occurs in Geone- 

 7nei'fespalaensis, 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 IJalacobdella, however, the proboscis-sheath opens into a 

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

 regarded as a veritable pharynx. Von Kennel ^ would have 

 us believe that the cavity of the proboscis-sheath opens into 

 the mouth in Geonemertes jpalaensis also ; but it appears to 

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

 condition is precisely the same as in Monogonoi^ora and 

 Frosadenoporus^ that is to say that the oesophagus opens into 

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

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



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

 nemertes chaHcojyJiora opens into the mouth. But on referring 

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

 clearly that the oesophagus opens into the proboscis-sheath at 

 a considerable distance from the external aperture of the 

 latter; it curves distinctly upwards^ 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 tiiough 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 csecal 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 zur Kenntnis der Nemertinen,"Arbeiteu aus 

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



t Von Graif, "Geonemertes chalicophora, eine neue Land-nemertine," 

 Morphol. Jahrb. Bd. v. 1879. 



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

 H.M.S. ' Challenger,' 1873-1876,' Zool. vol. xix. Nemertea, ISS?." 



§ Max Miiller, ' Observationes Aaatomicce de Vermibus quibusdam 

 maritimis,' Berolini, 1852. 



