278 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
they assist in increasing the tilt; then the next feet 
in the series lay hold, and so on, till the globe 
slowly but steadily rises upon its equator (Fig. 51). 
The difficulty of raising such a heavy mass into 
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Fig. 51. 
this position by means of the slender motive power 
