HOMES UNDEK THE SEA. 

 CHAPTER VI. 



SEA URCHINS MATERIAL AND DEVELOPMENT. 



THERE is yet another point in the structure of these 

 wonderful beings, the Sea Urchins, which we must 

 consider. 



The}'- may be found of all sizes, from that of a pea to 

 that of a melon. They retain the same shape throughout 

 their lives, and therefore must have some means of 

 increasing in size with absolute regularity. The solution 

 of this problem may readily be found by opening the 

 Urchin and looking at the inside of the shell. Thus 

 the structure will then be seen to consist of hexagonal 



plates, two sides being very much longer than 



the others. Each plate is slightly hollowed. 

 The interior of the shell is lined with a membrane 



