OF NATURAL HISTORY. t4i 



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

 known multivalved fhell-fi(h, merits our attention. This animal, 

 of which there are feveral fpecies, is round, oval, or fliaped hke a 

 bias-bowl. The furface of the fhell is divided into beautiful trian- 

 gular compartments, and covered with numberlefs prickles; from 

 which laft circumftance it has received the appellation oi fea-urchin, 

 or fea- hedge- hog, Thefe triangles are feparated by regular belts, and 

 perforated by a great number of holes. Each hole gives lodgement 

 to a flelhy 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 (hell, 

 the fea-urchin is enabled to walk either on its back or on its belly. 

 The limbs it moft generally employs are thofe which furround the 

 mouth. But, when it choofes, it can move forward, by turning on 

 itfelf like the wheel of a coach. Thus the fea-urchin furniflies an 

 example of an animal employing many thoufand limbs in its various 

 movements. The reader may try to conceive the number of mufcles, 

 of fibres, and of other apparatus, which are requifite to the progref- 

 five motion of this little animak 



The motion of that fpecies of medufa, or fea-nettle, which at- 

 taches itfelf to rocks, and to the larger fliell-fifh, is extremely flow. 

 The fea-nettles afTume fuch a variety of figures, that it is impoflible 

 to defcribe them under any determinate fhape. In general, their 

 bodies have a refemblance to a truncated cone. The bafe of the 

 cone is applied to the rock, or other fubftance to which they adhere. 

 With regard to colour, fome of them are red, fome greenifh, fome 

 whitifh, and others are brown. When the mouth, which is very 

 kraie, is expanded, its margin is furrounded with a great number of 

 flefhy filaments, or horns, fimiiar to thofe of the fnail. Thefe horns 



are 



