312 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
one, lateral and downwards, till the animal assumes 
its normal position with its oral pole against the 
perpendicular tank wall. So considerable is the 
rotation in the downward direction, that the normal 
position is generally attained before one complete 
lateral, or equatorial, rotation is completed. 
The result of this experiment, therefore, implies 
that the righting movements are due to something 
more than the merely successive action of the series 
of feet to which the work of righting the animal 
may happen to be given. The same conclusion is 
pointed to by the results of the following experi- 
ment. 
A number of vigorous Echini were thoroughly 
shaved with a scalpel over the whole half of one 
hemisphere, «ze. the half from the equator to the 
oral pole. They were then inverted on their ab-oral 
poles. The object of the experiment was to see 
what the Echini which were thus deprived of the 
lower half of three feet-rows would do when, in 
executing their righting manceuvres, they attained 
to the equatorial position and then found no feet 
wherewith to continue the manceuvre. The result 
of this experiment was first of all to show us that 
the Echini invariably chose the unmutilated feet- 
rows wherewith to right themselves. Probably this 
is to be explained, either by the general principle 
to which the escape from injury is due—viz. that 
injury inflicted on one side of an Echinoderm 
stimulates into increased activity the locomotor 
organs of the opposite side,—or by the consideration 
that destruction of the lower half of a row very 
