292 THE OCEAN WORLD. 



worm-like cylinder ; its dimensions are so variable that, while some 

 species are only an inch or two in length, others attain thirty and 

 even forty. In general, the skin of the Holothuria is thick and 

 leathery ; it includes muscles, and is armed occasionally with small 

 projecting hooks or fangs, which enable the creature to hang for a 

 few seconds on to foreign bodies. From this coriaceous envelope 

 issue tentacular feet analogous to those described in the sea-urchin 

 and sea-star. 



When we open a Holothuria we find nearly the whole internal 

 cavity occupied with little white tubes. We know that the fabulous 

 cucumber spoken of in the "Arabian Nights " was stuffed with pearls 

 by the talking-bird. With our poor animal this, alas ! is not so. 

 These are no pearls, but simple prosaical tubes containing the ova. 

 The mouth opens at the extremity of the body ; it forms a sort of 

 funnel, and is surrounded, as by a glory, with an elegant circle of 

 tentacula. In the living animal, when it feels itself in security, these 

 tentacles expand themselves like the corolla of a flower. When the 

 fisherman seizes a Holothuria in the water this crown of tentacles 

 ceases to appear, for the animal has the power of withdrawing it quite 

 suddenly, and now it resembles nothing so much as a common leech. 

 If, however, it is preserved in fresh sea- water and left in peace if we 

 treat it, in short, with the regard due to its elegant crown of tentacula 

 this elegant ornament will be expanded in all its glory. Immediately 

 below the mouth is a muscular pharynx, which is contained in a long 

 intestine, with many convolutions, which terminate in the posterior 

 part of the body in an orifice whence is thrown from time to time a 

 little jet of water. The terminal portion of the intestinal canal in 

 these animals is enlarged, introducing us to a system of numerous 

 tubes which branch off into the visceral cavity, receiving the water 

 from without while breathing by its posterior extremity ; the animal 

 can at will fill this reservoir or eject the water, and it is by these alter- 

 nate movements of aspiration and its reverse that it renews the oxygen 

 necessary for respiration. The circulation appears to form a complete 

 circle, there being no heart or central agent ; but a ring round the 

 gullet, from which issue five principal nervous chords, represents the 

 nervous system. 



The Holothurias are of separate sexes, and they differ from the sea- 

 urchins and asterias in this : that their larvae are converted bodily into 



