THE SEA-URCHIN 



43 



till they die and decompose, as baits to attract clouds 

 of Infusoria, which, multiplying in the vicinity of the 

 urchin, may afford it an abundant supply of food.' 



Fig. 7. The Echinus, or Sea-Urchin. The Spikes removed. 



Hundreds of other points of interest in the struc- 

 ture and life history of the echinus might be men- 

 tioned ; but as there are special monographs written 



