SEA-URCHINS. 165 



the same use, especially in the lower classes of animals. 

 Both spines and suckers may come into play when the 

 animal is crawling among stones or living in holes, the sides 

 and roofs of which would form fulcra. The suckers are 

 used in attaching the body to rocks, by which means the 

 animal fixes himself firmly in his chosen position. 



Professor Agassiz indeed asks, " How in fact could these 

 small tentacula, situated as they generally are in that part 

 of the body which is never brought into contact with the 

 ground on which the animal moves, and overhung by cal- 

 careous solid spines ; how, I ask, could these flexible tubes 

 be used as organs of motion ?" The Professor further re- 

 marks, ^''It is an undeniable fact, and I have observed it 

 myself, that it is with their spines that the Echini move 

 themselves, seize their prey, and bring it to their mouths, 

 by turning the rays of their lower edge in different direc- 

 tions. But the correction of an error respecting the func- 

 tions of the ambulacral tubes does not solve the problem 

 relating to their nature and use. This problem we are yet 

 unable to solve, as we know nothing more respecting them 

 than that they are connected with the aquiferous system." 



One Professor however may be as good as another in 

 such a matter, if both have equal opportunities of observa- 



