THE SEA CUCUMBERS 



3281 



there is a sort of funnel or scoop formed 05' the short tentacles, while a few of the 

 tube feet form long horns or feelers on the upper side. In the deep-sea Psychropotes, 



on the other hand, mouth, vent, 



and tube feet are confined to a flat 



sole; while the posterior part of the 



body is extended in a long tail. 



Some holothurians live in mud; 



and by reason of constantly keep- 

 ing both mouth and vent above the 



surface their bodies have become 



curved in U-fashion, as seen in the 



U-shaped Ypsilothuria (illustrated 



on p. 3279). This is carried still 



further in the club-like Rhopalodina 



(illustrated on this page), a form 



shaped like a cherry, with a thick 



stalk; the openings of both mouth 



and vent being at the top of this 



stalk. A yet stranger modification 



CLUB-UKE SEA CUCUMBER, 



Rhopalodina, (natural size). 



is the holothurian described under the name Pelagothuria, 



which lives in the East Pacific, on 



the surface of the ocean. It has no 



calcareous spicules, the longitudinal 



muscles being mostly changed into a 



jelly tissue. Around the mouth the 



body is extended into a kind of disc, 



prolonged into thirteen to sixteen feel- 

 ers. The animal swims by the move- 

 ments of this disc. 



Holothurians have no means of 



offense, but protect themselves for 



the most part by assuming the color 



of their surroundings. The huge 



Synapta besseli, which reaches a length 



of six feet, has a habit, when taken 



in the hand, of squeezing the fluid contents of its body to- 

 ward the portion that is grasped, till it becomes too big to 

 hold. Some, when much irritated, seem to fade away 

 and dissolve by breaking up their tissues; while others 

 have an objectionable habit of shooting out a part of their 

 intestines in long viscous strings; and it is owing to 

 this that a common British form has gained the name cot- 

 ton spinner. It has been suggested that this habit has 

 been acquired in connection with the presence in the in 

 testine of small parasites, and these in their turn have their 

 206 



A DEEP-SEA HOLOTHU- 

 RIAN, Psychropotes. 

 (Two-thirds natural size.) 



A PLATED HOLOTHURIAN 



(Psoltts). 



Some plates of the back, above 

 the brood pouch, are removed 

 (enlarged three times'). 



