C62 



ECHINODERMA— CLASS HOLO THUROIDEA. 



(M) at the anterior end, and the anus (As) at the posterior. The row of 

 tube-feet passes down the middle of the under surface, between the mouth 

 and anus. On either side of these tube-feet, and well seen in the side-view, 

 is a row of podgy stumps, by which the animal moves as a centipede moves 

 by its legs. Behind the anus a part of the body is prolonged into a flat tail. 

 These animals live on the ooze of the abyssal ocean, gorging themselves 

 therewith. Some of the holothurians that live in the sand of the deep sea, 

 by constantly keeping both mouth and anus above the surface of the mud, 

 have had their bodies curved in U-fashion, and in one genus the two openings 

 have come to lie close together at the top of a thick stalk, so that one may 

 compare the animal to a conjuror's bottle with a divided mouth. A yet 

 stranger modification of the holothurian type is the beautiful Pelagothuria, 

 represented in Fig. 12 ; this lives in the East Pacific on the surface of the 

 ocean. It has no calcareous spicules, and the longitudinal muscles are mostly 

 changed into a jelly tissue. Around the mouth is a circlet of short tentacles 

 (T) ; and from these radiate thirteen to sixteen long feelers (R), the bases 

 of which are united by a web forming a disc, by which the animal swims in 

 much the same way as a floating jellyfish. The rest of the body, with the 



anus (As) at the end of it, hangs vertically 

 downwards. In life the semi-transparent 

 body is tinged a purplish red. 



Holothurians are of interest to men, 

 especially Chinamen, as furnishing a food 

 known as Trepang, which ranks with edible 

 birds' nests among the delicacies of the celes- 

 tial table. The fishing for this takes place in 

 the East Indies and along the Barrier Reef 

 of Australia. Only those species that have 

 few calcareous spicules are of value for this 

 purpose, while others are rejected because, 

 when caught, they get rid of all their insides. 



Ckinoidea (Sea-lilies). 

 The echinoderms that we have hitherto 

 discussed have all availed themselves, to a 

 greater or less extent, of their power of free 

 locomotion. The crinoids, on the other hand, 

 together with the extinct blastoids and some 

 of the cystids, are for the most part attached, 

 either during youth or for the whole of their 

 existence, to the sea-floor by means of a jointed 

 stem (Fig. 13). The body of the crinoid, which 

 is relatively small, is placed on the top of 

 this stem, and from it there extend long arms 

 which are usually branched and often provided 

 with yet smaller branches regularly arranged 

 along them, and called pinnules. Each of 

 the pinnules, or each of the finer divisions of 

 the arms, is provided on the upper side with a aroove, carpeted by the 

 minute rapidly waving processes known as cilia. These constantly drive a 

 stream of water down the groove towards the main arm, which is provided 



T v,"'j^'""''"^-^"^°'^^®" '^^^^ '^^^^'^ ''®^'^ pusses down the arms towards 

 the body, and is then carried down five similar grooves, one leading from 



Fig. 13.— Eestoeation of a fossil 



ClimOlB KROM THK WKNI.OCK LiMB- 



STONK {Botri/oerinus dacadacty- 

 lus). Two-thirds natural size. 



