18 ECHINODERMATA. 



of all his problems is obtained. Still, do not these incidents exhaust the 

 perils of disappointment. Some of the most interesting objects which 

 have roused our curiosity prove of such rarity, that even a second speci- 

 men cannot be obtained after the first, to complete our observations ; 

 or the continuity is lost with the lapse of tune. Sometimes the services 

 of an accomphshed artist are not to be procured at the critical moment, 

 when they would be most essential ; and at length, amidst numberless ob- 

 structions, the subject deemed so precious, perishes spite of all precaution. 



Personal experience enables me to testify, that, from similar causes, 

 the investigation of the nature of particular objects lias been more than 

 once interrupted for ten, nay for twenty years. 



Although it be the ordinary disposition of mankind to relish a far- 

 ther acquaintance with what is already famihar to them in part, I shall 

 venture hei'e to introduce some products of a less common kind, whereof 

 most of the learned, the curious, and inquisitive, are usually denied 

 all knowledge. 



HoLOTHURiA. — A class of animals has been constituted by later 

 naturahsts under the name of Echinodermata, which, strictly inter- 

 preted, is probably meant to infer Hedge-hog skins, or Rough skins. 

 Herein are included thi'ee different genera whereon I propose to make a 

 few observations — the Holothuria, Asterias and Echinus, though the name 

 is inappUcable to any but the last, for neither of the others have any 

 such corresponding characters ; and if I be right in the etymology, I 

 cannot comprehend how they could be associated with it. 



Naturalists have been greatly embarrassed, both in determining the 

 real structure of the Holothuria, and in assigning to it its positive posi- 

 tion in the Systema Naturce ; nor have they been more successful, in as 

 far as I am aware, in ascertaining the habits of the race. Those appa- 

 rently among the best qualified for settUng such important points, by 

 the preservation of hving specimens, if ever they had them in view, 

 have certainly contributed to their own disappomtment by premature 

 dissection : or they have been unable to obtain specimens in healthy and 

 vigorous animation. Hence the uniform prevalence of the most indis- 



