STAR-FISH AND SEA-URCHINS. OTF 
latively feeble ambulacral feet. It is, therefore, 
scarcely surprising that unless the specimens chosen 
for these observations are perfectly fresh and 
vigorous, they are unable to right 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 
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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, 
13 
