286 



THE OCEAN WORLD. 



suckers, with which they attach themselves. In certain circumstances 

 the animal walks by turning upon itself, like a wheel in motion." 



Nothing is more curious than to see a sea-urchin walk upon smooth 

 sand. But for the colour, it might he mistaken for a chestnut with 

 its bristling envelopes, the spines serving as feet to put the little round 

 prickly mass in motion. They have even been observed to form 

 themselves into a ball, and roll along like a globular fagot of prickles. 



One of the most singular organs of 

 the sea-urchin is its mouth. It is 

 monstrous. Placed underneath the 

 body it occupies the centre of a soft 

 space invested with a thick resisting 

 membrane : it opens and shuts inces- 

 santly, showing five sharp teeth (Fig. 

 115) projecting from the surface, the 



Fig.ii5. Buccaiarmatureof Echinus iividus. ed g es meeting at a point, as repre- 

 sented here, supported and protected 



by a very complicated framework, which has received the name of 

 Aristotle's Lantern (Fig. 116). Fig. 115 represents Echinus Uvidus 



in its normal state ; the 

 other shows the masti- 

 catory organs, that is to 

 say, Aristotle's Lantern. 

 To give the reader a 

 more complete idea of the 

 buccal organ in the sea- 

 urchin, let him glance at 

 one from the southern 

 seas, Clypeaster rosaceus, 

 represented in Fig. 117, 

 an outline of the entire 

 animal, the buccal appa- 

 ratus being placed under the shell, which has been broken in Fig. 116, 

 so as to lay this organ bare. 



The shape of the Clypeaster rosaceus is oval, straighter in front, 

 and thick and rounded at the edges. It is more common and more 

 largely distributed than any other living species, and it is supplied 

 with four or six ambulacra, or feet. 



Fig. 116. Masticating apparatus of Echinus lividus. 



