184- ECHINODERMATA. PART m. 



the whole length of the animal. Nerve-chords from the 

 ring at the gullet accompany these, and such is the irri- 

 tability of this muscular system, that the Holothurise 

 eject their viscera when alarmed or caught; but they 

 have the power of reproducing them: sometimes they 

 divide their whole body into parts. 



The respiratory organs are two very long and beau- 

 tifully arborescent tubes veined with capillary blood- 

 vessels. The circulation of the blood is similar to that 

 of the star-fishes, but more complicated. 



The minute calcareous particles scattered indepen- 

 dently in the tough leathery skin of the Holothuridse 

 remain as fine dust when the flesh is dissolved and 

 washed away ; but, upon microscopic observation, Mr. 

 Gosse found that the forms of these particles are re- 

 markable for elegance, regularity, and variety of struc- 

 ture, but that the normal form is an ellipse of open work 

 built up of five pieces of a highly refractive, transparent, 

 glassy material, having the shape of dumb-bells. 



The Holothurise found under stones at low spring tides, 

 on the British coasts, are small ; those dredged up from 

 deep water are five or six inches long, and not unlike a 

 well-grown warty cucumber ; they do not form an ar- 

 ticle of food in Europe, but they are highly esteemed 

 by the inhabitants of the Indian Archipelago and in 

 China, where many shiploads of the trepang are imported 

 annually. It is a species that swarms in the lagoons of 

 the coral islands, the reefs of the coral seas, and at Ma- 

 dagascar. Some species are two feet long, and six or 

 i eight inches in circumference. 



The order of the Holothuridse form eggs like all the 

 other Echinoderms ; the larval zooid has the same form 

 as that of the star-fishes, and changes its form twice, 

 while the members of the Holothuria are forming 

 within it ; at last they combine with those of the zooid, 

 and no part is cast off. 



