THE SEA URCHIN in 



PLATE XXXVIII 



THE SEA URCHIN (i and 2) 



The "urchin," as of course you know, is a 

 common country name for the hedgehog; and 

 the Sea Urchin is so called because it is covered 

 all over with long spikes, just as a hedgehog 

 is. These spines, however, are very easily broken 

 off, and when the animal dies, and its empty 

 shell is tossed to and fro by the waves, they are 

 knocked off in a very short time; so that when 

 you meet with a sea urchin's shell lying upon 

 the shore you nearly always find that it is 

 covered with nothing more than hundreds of very 

 tiny pimples. 



Now it is upon these little pimples that the 

 spines grow. If you were to examine one of the 

 spines with a magnifying-glass you would find 

 that its base was hollow. This hollow base is 

 just large enough to fit over one of the pimples, 

 to which it is fastened by a strong but rather 

 elastic muscle. So a sea urchin is able to move 

 its spines about quite freely. Indeed, it some- 

 times walks with them as well as with the little 

 sucker-feet, which it pokes out through tiny 

 holes in the shell just as a starfish does, mov- 

 ing a few forward at a time, and so hitching 



