MOTIONS OP ANIMALS. 107 



cies of sensations. The Abbe Dicquemare, however, has 

 shown, that it can perform movements perfectly correspond- 

 ing to its wants, to the dangers it apprehends, arid to the ene- 

 mies by which it is attacked. Instead of being destitute of all 

 sensation, oysters are capable of deriving knowledge from ex- 

 perience. When removed from situations which are constantly 

 covered with the sea, devoid of experience, they open their 

 shells, lose their water, and die in a few days. But even 

 when taken from similar situations, and laid down in places 

 from which the sea occasionally retires, they feel the effects of 

 the sun's rays, or of the cold air, or perhaps apprehend the at- 

 tacks of enemies, and accordingly learn to keep their shells 

 close till the tide returns. Conduct of this kind plainly indi- 

 cates both sensation and a degree of intelligence. 



The progressive motion of the sea-urchin, or sea-egg, a 

 well-known multivalved shell-fish, merits our attention. This 

 animal, of which there are several species, is round, oval, or 

 shaped like a bias-bowl. The surface of the shell is divided 

 into beautiful triangular compartments, and covered with num- 

 berless prickles ; from which last circumstance it has received 

 the appellation of sea-urchin or sea-hedgehog. These trian- 

 gles are separated by regular belts, and perforated by a great 

 number of holes. Each hole gives lodgment to a fleshy 

 horn,* similar to those of the snail, and susceptible of the same 

 movements. Like the snail, the sea-urchin uses its horns 

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

 rocks, stones, or the bottom of the ocean. By means of the 

 horns and prickles, which proceed from almost every point of 

 the shell, the sea-urchin is enabled to walk either on its back 

 or on its belly. The limbs it most generally employs are 

 those which surround the mouth. But, when it chooses, it 

 can move forward by turning on itself like the wheel of a 

 coach. Thus the sea-urchin furnishes an example of an ani 

 mal employing many thousand limbs in its various movements. 

 The reader may try to conceive the number of muscles, of 

 fibres, and of other apparatus, which are requisite to the pro- 

 gressive motion of this little animal. 



The motion of that species of medusa, or sea-nettle, which 

 attaches itself to rocks, and to the larger shell-fish, is extremely 

 slow. The sea-nettles assume such a variety of figures, that 

 it is impossible to describe them under any determinate shape. 

 In general, their bodies have a resemblance to a truncated 



* See Introduction, p. 82. * 



