STAR-FISH AND SEA-URCHIXS. 277 



latively feeble ambulacral feet. It is, therefore, 

 scarcely surprisino- that unless the specimens chosen 

 for these observations are perfectly fresh and 

 vigorous, they are unable to riglit themselves at 

 all ; they remain permanently inverted till they 

 die. But if the specimens are fresh and vigorous, 

 they are sooner or later sure to succeed in right- 

 ing themselves, and their method of doing so is 

 always the same. Two, or perhaps three, adjacent 

 rows of suckers are chosen out of the five, as the 

 rows which are to accomplish the task (Fig. 49). As 



iilll|lNII|lllil||![iiIplll|l||l|l|||||||iiill!ll|ilil!i l|||l|i| illllllllllll|ll|i|lll|!|l|llll|l|||K^^^ 

 Fig. 49. 



many feet upon the rows as can reach the floor of 



the tank are protruded downwards and fastened 



firmly to the floor; their combined action then 



serves to tilt the globe slightly over in their own 



direction, the anchoring feet on the other or 



opposite rows meanwhile releasing their hold of the 



tank to admit of this tilting (Fig. 50). The effect 



of this tilting is to enable the next feet in the 



active ambulacral rows to touch the floor of the 



tank, and, when they have established their hold, 

 19 



