Marvels of the Universe 



469 



nigh even'thing about 

 arranged 



Here represented 

 is esteemed as food i 

 like an egg. 



THE COMMON SEA-URCHIN. 



Common 



about half the natural s 

 1 ih'e countries round the 



Med 



1 terranean. 



[/;. Sle/i, F.L.S. 



all our shores, it 

 where it is cooked 



potter}', fashioned out of a 

 lump of plastic clay, can com- 

 pare with this natural box 

 of eggshell -ware built up of 

 nearly six hundred pieces, all 

 fitted together edge to edge 

 with such nicety that there is 

 not a hair's space between 

 them. And yet this ware is 

 only about one-twenty-fourth 

 of an inch in thickness ! 



A remarkable feature of 

 this structvu-e is seen in the 

 five-sided character of all the 

 little plates that go to make up 

 the cupola-like box. The Sea- 

 Hog, in truth, is built up on a 

 pentamerous system. Well 



it is 

 in fives or some 

 multiple of five. Turn it over, 

 and you will see that its mouth 

 — which is lowermost — is guarded by the tips of five white teeth, which meet in a common point. 

 Then the plates of which the box is composed are arranged in bands according to their size and 

 character ; these are of three kinds and there are ten bands of each. The smallest of these plates 

 are perforated with a large number of minute holes which are arranged in pairs, and there are 

 three pairs in each row. Other plates bear spines, which are attached by cup-and-ball socket- 

 joints to solid polished bosses 

 on the plates, the spine and 

 the boss being held together 

 by a muscular band which 

 moves the spine in any direc- 

 tion. When an Urchin has 

 been denuded of its spines 

 these Uttle bosses will be seen 

 standing out in regular rows 

 from the sheU. 



In order to manipulate 

 these spines, and for other 

 purposes, the outside of the 

 box is coated with a layer 

 of thin flesh, which is very 

 sensitive. Touch it gently 

 with any slender instrument 

 that win pass between the 

 spines without touching them, 

 and immediately every spine 

 in that area wiU turn its point 

 towards the spot touched. At 



J'li„IO blf] 



[/■:. SI, -/J. r.L.s. 



FLEMING'S SEA-URCHIN. 



most beautiful of the British Urchins, it 



This is. perhaps, th 

 being particularly graceful. They are an inch 

 three inches across, and nearly as high. 



and i 



long sharp spines 

 half long, whilst the "shell" is 



