ECTIINODEIIMATA. 179 



bowels. It is in fact extremely difficult to obtain perfect speci- 

 mens of tlie Holothuridse, from the constant occurrence of this ac- 

 cident : but, although annoying to the naturalist, such a pheno- 

 menon affords the physiologist an important lesson, teaching that 

 here, as in the lower Zoophytes, the muscular system possesses an 

 innate contractile power, which would seem only to be destroyed 

 by incipient putrefaction ; but so little is this contractility under 

 command, that, once excited to an inordinate extent, it becomes 

 totally unmanageable, even though its continuance inevitably causes 

 the destruction of life. 



(220.) Fistularida. In order to complete our account of the 

 organization of the Echinodermata, we have still to investigate the 

 structure of the Fistularid<z ; a group which, from the external 

 appearance of the individuals composing it, and the total absence of 

 the tubular feet met with in other families, has been improperly 

 separated by some modern writers from the class under consideration. 

 Nevertheless, we shall find the position assigned to these animals by 

 Cuvier to be in strict accordance with the character both of their 

 outward form and internal structure ; only, instead of placing them 

 with the lowest of the Echinoderms, they would have been more 

 properly situated at the head of the class, as most nearly ap- 

 proximating the Annelida in all the details of their economy. We 

 have already given a description of the outward form of a Fistu- 

 laria ( 186), and seen the completely annulose condition of its 

 body, although the radiating tentacula around the mouth are evi- 

 dently analogous to those of the Holothuria already described. We 

 are indebted to the patient researches of Pallas and Delle Chiaje* for 

 almost all that is known concerning the anatomical structure of these 

 animals, and the descriptions of the Siponculus phalloides and bala- 

 nophorus have left little to be desired by the systematic zootomist. 



The Siponculus inhabits shallow seas, concealing itself at the 

 bottom in holes which it excavates in the sand. Having once 

 located itself, it is seldom found to quit its concealment, but, re- 

 taining its hold upon the sides of the retreat which it inhabits by 

 dilating the posterior part of its body, it occasionally protrudes its 

 head from the orifice, either for the purpose of procuring food, or 

 of respiring more freely the element in which it lives. 



These animals are much sought after by fishermen, who employ 

 them as baits for their hooks ; and one species, Siponculus edulis, 

 is used in China as an article of food. 



* Storia e Notomia delle Animate senza Vertebre del Regno di Napoli. Napoli, 1823. 



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