38 HIDDEN BEAUTIES OF NATURE 



Apart from the spines to which we have referred, 

 the box or case of the echinus, deprived of spikes and 

 thoroughly washed on both sides, is a very beautiful 

 structure. It consists of a multitude of plates beauti- 

 fully fitted together, and arranged to grow larger as 

 the creature grows. Considering the thinness of the 

 plates and the extremely light weight of the structure, 

 there are few objects of its size that will stand equal 

 strain. Every part of the echinus will bear the 

 closest examination, and will prove sufficient for study 

 for a long time. The people along the shores of the 

 Mediterranean eat the contents of these echinus boxes. 

 They are sold in the markets with other products of 

 the sea. 



Professor A. Agassiz tells us in his Report on the 

 Echinoidea, or sea-urchin tribe, that there are 2,300 

 known species of fossil and recent echinids. His 

 report contains 321 pages of descriptive matter in 

 addition to 45 plates of illustrations. This will show 

 the extensive character of this one department of 

 Natural History. Some members of this vast family 

 are always to be found washed up on all sea-shores 

 from the poles to the equator. We ought, therefore, 

 to have little difficulty in procuring specimens for 

 examination. In the fossilized state they may be 

 picked up in any district where chalk is the pre- 

 vailing rock. Frequently we find them on the 

 roads with the flints, doing duty as road material. 

 Going back to still earlier geological formations, 

 we find splendidly preserved representations in the 



