AMBUXACKAL TUBES. 293 



prey, and bring it to their mouths by turning the 

 rays of their lower edge in different directions. But 

 the correction of an error respecting the functions of 

 the ambulacral tubes does not solve the problem re- 

 lating to their nature and use. This problem we are 

 yet unable to solve, as we know nothing more re- 

 specting them than that they are connected with the 

 aquiferous system/ 



Many other writers, among whom is Professor 

 Forbes (from whose work on Star-fishes I have 

 transferred the foregoing extract), assert, in opposition 

 to the great Swiss naturalist, that the Echinidae move 

 by the joint action of their suckers and spines. ' The 

 argument/ says the great British naturalist, 'against 

 the suckers being organs of motion, founded on their 

 position above as well as below, would equally apply 

 to the spines, to which organs Professor Agassiz 

 has attributed all progressive powers in these 

 animals/ 



The fact is now so well established, that it is 

 scarcely necessary for the writer to state, that from 

 personal observation he can fully confirm the evidence 

 of Professor Forbes relative to the functions of the 

 suckers of the Sea-Urchins. But although that 

 talented author entertained no doubt as to the organs 

 in question being powerful locomotive agents, he 

 evidently seems to have felt himself unable to sug- 

 gest any purpose they could possibly serve when 

 situated on the back or upper part of the animal. 



