398 Dr. O. Burger on the 



at the same time a cleft appears on each side between intes- 

 tme and parenchyma {Cerebratulus margin at us an([ Drepano- 

 phorus serraticollis). This cleft is interrupted at the points 

 at which the extremities of the intestinal cffica come in contact 

 "with the septa, and also where those plates which include the 

 genital sacs and the dorso-ventral muscle-bands touch the 

 axial portion of the intestine. This cleft was pronounced by 

 Salensky "^j who determined its existence in Monopora vivi- 

 jpara and Eiqjolta aurita^ to be a coelom. Salensky finds 

 that it is bounded by a somatic and splanchnic membrane. 



The Turbellaria are devoid of cavities of this kind lying 

 between the tissue of the body and the intestine. On the 

 other hand, muscular septa are present, and in this respect 

 the elongated Gunda segmentata f is especially worthy of 

 notice, since in it the lateral unbranched intestinal caeca are 

 regularly separated from one another in this way. In the 

 other direction, however, the pronounced metameric arrange- 

 ment of the septa in Nemertines leads us to the Annelids, and 

 to the Hirudineai in particular, in which, while a body-cavity 

 is non-existent, muscular sej)ta are developed. 



The alimentary canal of the Nemertines exhibits two 

 divisions, which are both histologically and morphologically 

 well marked off from one another : these are, the fore-gut, 

 which is devoid of Cffica in all forms, but is lined by a richly 

 glandular epithelium, and the mid-gut, which in the two last 

 groups is provided with metamerically arranged paired 

 evaginations, but is without glands. The intestinal caeca 

 decrease gradually in size towards the posterior extremity of 

 the animal, and finally we get a little short piece of intestine, 

 straight and without glands, which we are able to distinguish 

 as rectum, but which nevertheless in the character of its 

 epithelial lining does not differ from the mid-gut. It is 

 therefore doubtful whether, without referring to embryology, 

 we are entitled to speak about a proctodaeum in the case of 

 the Nemertines. The mouth is always ventral in Groups I. 

 and II., behind or beneath the ganglia, and opens into an 

 expanded, bell-shaped, pharyngeal cavity — in the case of 

 Group III. in front of the ganglia — which in its turn opens 

 into a narrow oesophagus. The mouth does not always open 

 independently to the exterior, but more often unites with the 

 aperture of the proboscis-sheath. In Monogonopora and also 

 in Prosadenoporus the oesophagus opens into the proboscis- 



* Salensky, " Zur Entwickelungsgeschiclite v. Borlasia vivipara,''^ Biol, 

 Centralbl. ii. Jahrg. 



. t A. Lang, " Der Bau von Gunda segmentata,'^ Mitth. a. d. Zool. 

 Station zu Neapel, Bd. iii. 1881. 



