REPORT ON THE NEMERTEA. 107 



* 



opposite each other. The epithelium which coats the internal cavity of the sheath is seen 

 to be continued uninterruptedly in these lateral spaces, whereas the musculature is deficient, 

 and these caeca may thus with propriety be called membranous. There is a decidedly 

 thicker epithelial coating in the lateral sacs of fig. 4 {Drepanophorus lankesteri) than in 

 those of fig. 5 [Drepanophorus serraticollis). On the other hand, the musculature of the 

 proboscidian sheath of the latter is much more massively developed than that of the 

 former. 



One remarkable detail concerning the lateral appendages in Drepanophorus lan- 

 kesteri, is the fact tbat I found a few of the anterior ones connected by a short longitu- 

 dinal communicating tube at their distal extremity, this connection being thus parallel to 

 the proboscidian sheath itself. Simdar connections were not noted further backwards, nor 

 in any other species of Drepanophorus. 



Whde the proboscidian sheath of Amphiporus marioni (PI. X. fig. 1) is built on 

 the same plan as that of Drepanophorus, that of Pelagonemertes is seen to be much 

 simpler (PI. VIII. fig. 7). Both are quite freely suspended in the gelatinous tissue, 

 and only connected with the body musculature in the head (PI. X. fig. 3). 



DIGESTIVE APPARATUS. 



The digestive canal of the Nemertea cannot be said, from a morphological point of 

 view, to be very complicated. 



Communicating with the exterior by a ventral mouth close behind the tip of the 

 head and by a terminal anus, it stretches along the whole length of the body, and only two 

 rather sharply defined regions may be distinguished in it : the oesophagus and the hind 

 gut or intestine proper. Still, even the mouth is not always an independent structure, 

 as it is known to become confluent with the opening through which the proboscis pro- 

 trudes, i.e., the terminal opening of the rhynchodaeum, 1 in at least two genera [Amphiporus 

 and 3IaIacobdella 2 ). In that case this common opening is either terminal or nearly so 

 (PI. IX. fig. 9), and generally larger than the separate openings in other Hoplonemertea. 

 This feature is clearly not primitive but derived from that condition in which the mouth 

 lies behind the brain-lobes on the ventral surface, as it does in the most primitive 



1 Rhynchodaeum (see p. 8) is the name that may conveniently be given to the passage stretching from the point of 

 insertion of the proboscis in the head to the level of the exterior opening on the surface of the body through which the 

 proboscis is seen to be thrust forth. Its walls are marked APe in fig. 5 of PI. III.; Rh. and Sp. Pr. in fig. 3, PI. X. 



* Salensky has lately (Biologisches Centralblatt, 1883, p. 740, and Archives de Biologic, vol. v.), in publishing embryo- 

 logical researches on a certain species of Nemertea, imagined that the feature here alluded to was then and there 

 discovered by him for the first time, and necessitated the creation of a new genus {Monopora). Although his attention 

 was drawn to the superfluity of this proceeding (XTV. p. 41), he still retains the name in a later publication (Zeitsclir. f. 

 vriss. Zool, Bd. xliii. p. 481). Still, I am afraid this will not extend its longevity, as all the other anatomical characters 

 most decidedly conform to Amphiporus. 



