OF NATURAL HISTORY. 149 



fea-water as Is fufficient to cover them. The oyfter has been 

 reprefented by many authors as an animal deflitute not only 

 of motion, but of every fpecies of fenlation. The Abbe Dic- 

 quemare, however, has fhown, that it can perform movements 

 perfectly confonant to its wants, to the dangers it apprehends, 

 and to the enemies by v»^hich it is attacked. Inftead of being 

 deflitute of all fenfation, oyflers are capable of deriving 

 knowledge from experience. When removed from fitua- 

 tions which are conftantly covered with the fea, devoid of ex- 

 perience, they open their fhells, lofe their water, and die in 

 a few days. But, even when taken from fimilar fituations, 

 and laid down in places from which the fea occafionally re- 

 tires, they feel the effects of the fun's rays, or of the cold 

 air, or perhaps apprehend the attacks of enemies, and accor- 

 dingly learn to keep their iliells clofe till the tide returns. 

 Condudl of this kind plainly indicates both fenfation and a 

 degree of intelligence. 



The progreffive motion of the fea-urching, or fea-egg, a 

 well known multivalved fhell-fifh, merits our attention. This 

 animal, of which there are feveral fpecies, is round, oval, or 

 fhaped like a bias-bowl. The furface of the fhell is divided 

 into beautiful triangular compartments, and covered with 

 numberlefs prickles ; from which laft circumftance it has re- 

 ceived the appellation of ^'^^-z/rr^/;/, or fea-hedge-hog. Thefe 

 triangles are feparated by regular belts, and perforated by a 

 great number of holes. Each hole gives lodgment to a flefhy 

 horn fimiiar to thofe of the fnail, and fufceptible of the fame 

 movements. Like the fnail, the fea-urchin ufes its horns 

 when in motion ; but their principal ufe is to fix the animal 

 to rocks, ftones, or the bottom of the ocean. By means of 

 the horns and prickles, which proceed from almoft every 

 point of the fhell, the fea-urchin is enabled to walk either on 

 its back or on its belly. The limbs it mofl generally employs 

 are thofe which furround the mouth. But, when it choofes, 



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