280 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 



But an Echinus will never let go its attachments 

 without some uro^ent reason, seemingr to be above 

 all things afraid of being rolled about at the mercy 

 of currents ; and therefore in this case it lets itself 

 down almost as slowly as it raised itself up. So 

 gently, indeed, is the downward movement effected, 

 that an observer can scarcely tell the precise 

 moment at which the ricrhtins: is concluded. There- 

 fore, in the downward movement, the feet, which at 

 the earlier part of the manoeuvre were employed 



lililllilillllllllllllli!llyiiniiii!,i'!'!!"i!!ill!!'l!'iiO 



Fig. 52. 



successfully in rearing the globe upon its equator, 

 are now employed successfully in preventing its too 

 rapid descent (Fig. 52). 



Several interesting questions arise with reference 

 to these righting movements of Echinus. First of 

 all we are inclined to ask what it is that determines 

 the choice of the rows of feet which are delegated 

 to effect the movements. As the animal has a 

 geometrical form of perfect symmetry, we might 

 suppose that when it is placed upon its pole, all the 



