REPORT ON THE HOLOTHURIOIDEA. 133 



can judge, possesses no aperture. I have not the least idea of the functions of this 

 cavity, but aggregations of corpuscles resembling blood having often been found 

 within it, it may possibly communicate with the pseudhsemal vessels. 



The digestive tract in Benthodytes sanguinolenta as well as in Benthodytes 

 sanguinolenta, var. marginata, is especially characterised by its second descending 

 portion carrying a large, wide csecal appendage or "diverticulum" about 15 mm. long 

 (PI. XL. fig. 4), which is situated far from the anus, in the largest individuals at 

 a distance of about 170 mm., and which opens within the digestive tract by a very wide 

 aperture ; its structure does not differ greatly from that of the digestive tract. 



Having nothing of importance to add to that which already is known, I think it 

 unnecessary to give an account of the histological structure of the walls of the alimen- 

 tary canal. I only refer to the Plate XXXVI., figs. 1 and 2, which represent some sections 

 showing the different layers which compose the walls. The digestive tract is often 

 strengthened by calcareous spicula of varying shape and size. 



The cavity or sinus, which is enclosed between the most anterior portion of the 

 digestive tract and the surrounding water-vascular ring with its five main branches, and 

 which is termed the " oesophageal sinus," is either almost entirely closed by a thin 

 membrane, as in Lcetmogone (PI. XLIII. fig. 4), Elpidia glacialis, Benthodytes 

 sanguinolenta (PI. XL. fig. 5), llyodcemon mactdatus, &c, or this membrane is absent 

 (PL XLIII. fig. 6), the sinus thereby communicating directly with the peritoneal 

 cavity, as in Oneirophanta, Orphnurgus, &c. 



Throughout the whole of its course, the alimentary tube is connected with the 

 wall of the body by a dorsal mesentery, which either, as in Oneirophanta, L&tmogone, 

 &c, consists of a continuous more or less fenestrated membrane, or, as in Scotoplanes 

 globosa, &c, is reduced to bands and threads. The mesentery is usually strengthened by 

 calcareous spicula of varying shape and size. 



The Pseudhsemal System. 



The pseudhsemal system in the Elasipoda closely resembles that in the rest of the 

 Holothurioidea ; and this having been already most carefully described by Tiedemann, 

 Semper, &c, does not require any further explanation. I only intend to point out 

 some peculiarities, especially with regard to the arrangement of the vessels, which in a 

 more or less important degree distinguish the order in question. However, it ought to 

 be remembered that any closer examination of the hasinal system has not been possible 

 because of the materials having been highly macerated and softened by long immersion 

 in spirit. 



The ventral and dorsal stems seem usually to consist of but a single vessel. None of 

 the Elasipoda possessing any respiratory trees, no traces are discernible of the large rete 



