SEA-URCHINS. 169 



seize the small animals which serve for its sustenance, partly 

 to lay hold of whatever might approach their sensitive skin, 

 which covers the surface of the shell, and thus, in conjunc- 

 tion with the prickles, protect it from injury/^ 



The specific characters of the Egg-Urchin are, a rounded 

 body ; ambulacra continuous from mouth to opposite open- 

 ing ; tubercles of spines imperforate, and spines all in one 

 form, numerous. It is generally of a purplish or reddish 

 colour, with spines nearly white, sometimes tipped with 

 purple. 



Shore collectors cannot obtain living specimens ; for it is 

 a deep-water animal, congregating in great numbers at sea- 

 bottoms. But now that the dredge is in active use, and it 

 has become a business to supply Aquarians with specimens 

 of marine zoology, we can get living Sea-Eggs " to order " 

 without stirring from our homes. 



'Echinus miliaris is a smaller species, with proportionally 

 larger spines, which are gTooved, pointed, and tipped with 

 purple. 



Spatangus purpureiis has the body depressed, heart- 

 shaped, with the mouth forwards and the anal vent back- 

 wards, so that the animal has both an anterior and a pos- 

 terior end. 



