ITS ORGANS OP MOTION. 177 



The Egg Urchin (Echinus sphcera) is so well known 

 that I scarcely need enter into a minute description of 

 its form. As commonly seen ornamenting the chimney- 

 pieces of cottages near the sea-side, it is a slightly-de- 

 pressed sphere, divided by five double rows of minute 

 holes (called ambulacra), into ten gore-shaped spaces, 

 of which each alternate one is twice as broad as the 

 other. These spaces are moreover studded with rows of 

 pearls, arranged with much regularity, and of various 

 sizes. When the animal was alive, a short white spine, 

 used by the Urchin as an organ of motion, or of de- 

 fence, was articulated by a socket-joint to each pearly 

 tubercle, which formed the ball on which it freely 

 revolved. From each pair of holes of the ambulacra 

 issued a sucker, like that of the Star-fish, and used for 

 the same purposes. So that the Urchin, which now 

 looks so armless and bald, was furnished with hundi-eds, 

 nay, thousands, of active organs, arms or legs, as he 

 required them. Nor were these by any means all the 

 apparatus with which he was provided. On the surface 

 of his coat, among the spines, were multitudes of ex- 

 ceedingly minute and beautifully-formed pincers, which 

 were in perpetual action, moving about from side to 

 side, and opening and shutting their three-forked apex 

 continually. These most singular organs, which are 

 also found on some Star-fishes, are called by naturalists 

 pedicellarice ; but their use to the animal is wholly 

 unknown, and by some writers they are described as 

 parasitic creatures of different species. I can hardly 

 so regard them, and, whatever their office may be, 

 must suppose them a part of the animal on which 



