316 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
in a vertical plane. The object of this was to 
ascertain whether the continuous rotation in a 
vertical plane would prevent the animal from right- 
ing itself (because confusing the nerve-centres 
which, under ordinary circumstances, could feel by 
their sense of gravity which was up and which 
was down), or would still allow the animal to right 
itself (because not interfering with the serial action 
of the feet). Well, it was found that this rotation 
of the whole animal in a vertical plane entirely 
prevented the righting movements during any 
length of time that it might be continued, and that 
these movements were immediately resumed as 
soon as the rotation was allowed to cease. This, 
moreover, was the case, no matter what phase of 
the righting manceuvre the Echinus might have 
reached at the moment when the rotation began. 
Thus, for instance, if the globe were allowed to 
have reached the position of resting on its equator 
before the rotation was commenced, the Echinus 
would remain motionless, holding on with its equa- 
torial feet, so long as the rotation was kept up. 
Therefore, there can be no question that the am- 
bulacral feet are all under the influence of a co- 
ordinating nerve-centre, quite as much as are the 
spines. But, on the other hand, experiments show 
that the centre in this case is not of so localized a 
character as it is in the case of the spines; for 
when the nerve-ring is cut out, the co-ordina- 
tion of the feet, although impaired, is not wholly 
destroyed. Take, for instance, the case of the 
righting manceuvre. The effect of cutting out the 
