HOLOTHURIANS. 



183 



' sions. H. marmorata, from the East Indian islands, Fijis, etc., reaches a foot in 

 length, and S. tenuissima attains a length of two feet, and a thickness of six or seven 

 inches. 



In some species of Holothuria, as in H. marmorata, the ambulacral processes of the 

 lower surface only are truly ambulacral feet, the others are papillae : in another group, 

 including H. tenuissima, the suckers or papillae are all alike, and in still another the 

 ambulacral feet upon the ventral surface are much closer together than those upon the 

 back. 



Holothuria floridana is abundant on the Florida reefs just below low-water mark, 

 and reaches a length of fifteen inches. The calcareous pharynx leads to an alimentary 

 canal which is .about three times the length of the body, and ends in a large cloaca. 

 The branch of the respiratory tree which is attached to the body-walls extends to the 



Fig. 161. — Cladodactyla crocea. 



pharynx. The Polian vesicles are numerous, the largest an inch in length, and the 

 madreporic body has upon it a group of about thirty stalked processes, the largest 

 about a quarter of an inch in length. The tentacular ampullas are twenty in number, 

 long and slender. 



Order IV. — DIPLOSTOMIDEA. 



This order, or sub-class, established by Semper to contain the singular Jihopalodina 

 lageniformis, is characterized by a nearly spherical body, with the mouth and anus 

 close together, and ten ambulacra. Semper regards it as the type of a fifth class of 

 echinoderms. 



Ehopalodina lageniformis has a flask-shaped body, and the mouth and anus are at 

 the narrow end of the flask, the former surrounded by ten tentacles, the latter by ten 

 papillae and by as many calcareous plates. A ring of ten calcareous plates surrounds 



