'2/6 THE OCEAN WORLD. 



at first, to find a reason for this designation. The corona or body of 

 the sea-urchin is furnished with different kinds of spines. It forms a 

 shell, nearly spherical, empty in the interior, its surface presenting 

 reliefs remarkable for their regularity. In order to see the urchin 

 with its spines it is necessary to seize it as it lives, in the water at the 

 bottom of the sea, where it rolls and moves its little prickly mass ; it is 

 then only that the real urchin — the prickly sea-urchin — is to be seen, 

 bristling with prickles, and strongly resembling, to compare the physical 

 with the mental, those amiable mortals whose character is so well 

 depicted in the saying, " Whom they rub they prick." 



In his book on " The Sea," Michelet puts the foUo^nng conver- 

 sation into the mouth of a sea-urchin : — 



" I am born without ambition," says the modest Echinoderm; "I 

 ask for none of the brilliant gifts possessed by those gentlemen the 

 molluscs. I would neither make mother-of-pearl nor pearls ; I have 

 no wish for brilliant colours, a luxury which would point me out; still 

 less do I desire the grace of your giddy Medusas, the waving charm of 

 whose flaming locks attracts observation and exposes one to shipwreck. 

 Oh, mother ! I wish for one thing only : to be — to be without these 

 exterior and compromising appendages ; to be thickset, strong, and 

 round, for that is the shape in which I should be the least exposed ; 

 in short, to be a centralised being. I have very little instinct for 

 travel. To roll sometimes from the surface to the bottom of the sea is 

 enough of travel for me. Glued firmly to my rock, I could there 

 solve the problem, the solution of which your future favourite, man, 

 seeks for in vain — that of safety. To strictly exclude enemies and 

 admit all friends, especially water, air, and light, would, I know, cost 

 me some labour and constant effort Covered with movable spines, 

 enemaes will avoid me. Now, bristling like a bear, they call me an 

 urchin." 



Let us now look a little more closely at the general structure of the 

 sea-urchin — in zoological language, Echinus. 



The body of the sea-urchin is globular in form, slightly egg-shaped, 

 or of a disc slightly swollen. It consists essentially of an exterior 

 shell, or solid corona covered with spines, and invested in a delicate 

 membrane furnished with vibratile cilia. This corona is formed of an 

 assemblage of contiguous polygonal plates, adhering together by their 

 edges. Their arrangement is such that the test or shell may be 

 divided into vertical zones, each springing from a central point on 

 the summit, and terminating at a point of the spheroid diametrically 

 opposite — namely, the circumference of the buccal orifice. These 

 vertical zones are of two kinds, some larger and others straighter, 



