THE TOMB OF PEARL 



accustomed place. Circumstances, that is to say the 

 arrangement of the organs in the sea cucumber, allow of 

 such strange comings and goings, which could not 

 happen anywhere else. 



The sea cucumbers are long-bodied Echinoderms, 

 with thick skins, roughened by the possession in their 

 substance of a number of calcareous concretions. They 

 have not carried this to the extent of other Echinoderms, 

 notably the sea-urchin, which has a regular suit of 

 armour surrounding its body. Their genera and species, 

 in considerable numbers, populate the waters of the 

 Mediterranean, where, because of their weight, they 

 live upon the bottom. Some of the sea cucumbers, 

 belonging to the genera Holothuria and Stichopus, 

 are frequent near the shore, and the fishermen often 

 bring them up, Holothuria like large black-puddings, 

 Stichopus like broad, thick, pink tongues. Sometimes, 

 some of them contain Fierasfers, especially Holothuria 

 tubulosa. 



In the sea cucumbers, the digestive tube has two 

 openings, one for each of the extremities of the 

 body, both spacious in the well-developed animal; 

 the mouth, surrounded by a crown of tentacles, 

 the anus, which is bare. The mouth gives access to 

 a long convoluted intestine, which, before it ends in 

 the anus, broadens out into a large rectal swelling. 

 Appended to this enlargement, and opening into it, are 

 two spacious tubular organs which look like hollow, 

 tree-like growths with very thin walls. Because of this 

 appearance they are sometimes called the Holothurian's 

 " lungs," for they are used for breathing. It would be 

 better to call them " gills," since the Holothurians live 

 in water and have to breathe in it. Their method of 

 working can be judged by the mode of their construction. 

 The skin of the Holothurians is not of much use for 

 breathing because it is so thick. So is the intestine, 

 which is filled with sand and little pebbles which the 

 creature swallows on the bottom, leaving to its diges- 

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