THE SEA-URCHINS. 163 
Among all the sights which Nature presents to us, there is 
scarcely one more interesting than that of creatures giving to 
each other shelter, and food, and protection, whether voluntarily 
or involuntarily. Is not the instinct of the stylifer marvellous? 
Nature has bestowed upon one creature an armour of bristling 
bayonets, when another animal, much smaller, seems to approve of 
the admirable defence, and takes up its abode in the midst—nay, 
AN ECHINUS CLIMBING UP THE SIDE OF AN AQUARIUM. 
actually in the spines, which, henceforth, protect itself as well as 
the urchin. 
When the bristles fall off, the echini are found on our shores, 
very much like round fruit, ornamented on the sides with tubercles, 
symmetrically arranged. Their round form, and, perhaps, especially 
the limy nature of their shells, has obtained for them the name of 
sea eggs. The flattened species, denuded of their spines, are more 
like cakes than eggs. 
The tentacule of the sea-urchins are hollow, very elastic, and 
Tey 
