SEA-CUCUMBERS. 



53 



upon which the Sea-urchins feed. They are, therefore, con- 

 stituted with a continual growth, as in the case of the gnawing 

 animals, and the points have all the hardness of enamel. Five 

 jaws, admirably adapted to act as grinders, are furnished 

 with bony pieces, ligaments, and muscles, so contrived and 

 arranged as to draw from Professor Rymer Jones the remark, 

 " these jaws, from their great complexity and unique structure, 



Fig. 34. SEA-URCHIN (INTERIOR). 



form perhaps the most admirable masticating apparatus met 

 with in the whole animal kingdom " (Fig. 34). 



One species of our native Sea-urchins is remarkable for its 

 habit of boring, principally into limestone rocks, and living in 

 the excavation thus formed. It is gregarious, and was found 

 in abundance by Mr. Ball and Mr. Thompson, when visiting 

 the south Isles of Arran, in 1834. " It is always stationary; 

 the hole in which it is found being cup-like, yet fitting so as 

 not to impede the spines. Every one lived in a hole fitted to 

 its own size the little ones in little holes, and the large 



Fig. 34. ANATOMY OP SEA-URCHIN (Echinus). 



a, Month, with tho teeth and jaws.- &, Oesophagus. c, Stomach, or first por- 

 tion of the intestine. d, Intestine. e, Ovary./, Ambulacral vesicles. g, Shell 

 with spines. 



