CHAPTER XVI. 
THE HOLOTHURIDE. 
IN the same family as the sea-urchins—the Echinodermata—are 
placed the sea cucumbers, or, to call them by their scientific name, 
the Holothuria. These very curious animals have the form of an 
elongated and worm-like cylinder, sometimes straight, sometimes 
curved. Their size varies from one to forty inches; the larger size 
being the more common. 
The sea cucumbers have a thick and leathery skin, which is 
occasionally transparent; more frequently, however, the skin is 
THE TUBULAR HOLOTHURIA. 
(Holothuria tubulosa.) 
granular, filled with calcareous particles. Out of this envelope 
appear tentacular feet, similar to those found in the echinus ; 
they are hollow, and very expansible, and furnished at their 
extremities with a species of sucker. The mouth opens at the end 
of the cylinder, and is surrounded by a circle of tentacles. This 
mouth has immediately beneath it an osseous ring, composed of 
ten or twelve calcareous pieces; it is, in fact, the fundamental 
ring of Aristotle's lantern, described in the last chapter; at the 
tail end of the animal is a second orifice, from which issues, from 
time to time, a jet of water. 
The holothurias inhabit deep waters; and, as their locomotion 
is very limited, they are seldom found far from their native rocks. 
When they do move, it is by means of a crawling motion pro- 
