XIX ASPIDOCHIROTA — ELASIPODA 57 I 



by the Chinese. The Trepang are caught in various parts of 

 the Malay Archipelago. They are cooked in sea water to preserve 

 them, dried in the sun, and boiled in fresh water repeatedly, till 

 all the salt is extracted. They are then dried and sent to market, 

 where they are used in making soup. 



Order II. Elasipoda. 



Holothuroidea with shield-shaped feelers, destitute of retractor 

 muscles ; all the podia have more or less pointed ends,^ but there 

 is a marked contrast between dorsal and ventral podia, and the 

 ventral surface is flattened so as to constitute a creeping sole. 

 No respiratory trees, at most a simple diverticulum of the intes- 

 tine ; frequently the primitive external madreporite is retained, 

 and contains several pores. 



A number of spherical sacs containing little spherical calcifi- 

 cations (otocysts) are attached to the nerve-ring in some genera. 

 Can these be metamorphosed sphaeridia of Echinoid ancestors ? 



The first member of this remarkable order to be discovered 

 was Mpidia, which was dredged in 1875 by the Swedish Arctic 

 Expedition, and described by Theel.^ The majority of the known 

 members of the order were discovered by the dredging expedi- 

 tion of H.M.S. " Challenger." The species composing it are, 

 with one exception, inhabitants of what may be termed the 



Fig. 258. — Ilyodaemon maculatus. x |. (After Theel.) 



abysmal depths of the sea. The exception alluded to {Ilyodae- 

 mon maculatus) is confined to the belt between 100 and 150 

 fathoms in depth. The well-marked sole and the absence of 

 suckers point to a life consisting of constant peregrinations over 



1 Genuine suckers appear never to be developed ; but the ends of the ventral 

 podia are sometimes rounded, sometimes slightly flattened. 



2 "Meraoire sur VElpidia nouveau genre d'Holothuries," K. Sv. Vet. Akad. 

 3iv. No. 8, 1877. 



