ON THE LOCOMOTOR SYSTEM OF ECH1N0DERM ATA. 875 
then by their traction tilting over the globe, till D, E, and F, are able to touch the 
floor, and so on ; or does the righting action depend upon nervous co-ordination ? 
We conclude that both principles are combined—the action of the pedicels being serial, 
but also assisted by nervous co-ordination. This conclusion is sustained, not only by 
the movements of an unmutilated Echinus when suspended by a thread against the 
wall of a tank, but also by the experiment of shaving off the spines and pedicels over 
one half of one hemisphere— i.e., the half from the equator to the oral pole. When 
then inverted and forced to use their mutilated pedicel-rows, the Echini reared them¬ 
selves upon their equators, and then, having no more pedicels wherewith to continue 
the manoeuvre, came to rest. This rest was permanent—the animal remaining, if 
accidents were excluded, upon its equator till it died. The question, then, here seems 
to resolve itself simply into this :—Is the mechanism of the pedicels so constructed as 
to ensure that their serial action shall always take place in the same direction ; for if 
it can be shown that their serial action may take place indifferently in either direction, 
it would follow that the persistency with which the partly-shaved Echini continue 
reared upon their equators, is the expression of some stimulus (such as a sense of 
gravity) continuously acting upon some central apparatus, and impelling the latter to 
a continuous, though fruitless, endeavour to co-ordinate the absent pedicels. If the 
pedicels are able to act serially in either direction, there is no more reason why a 
partly-shaved Echinus should remain permanently reared upon its equator, than that 
it should remain permanently inverted upon its pole ; and therefore the fact that in 
the latter position the pedicels set about an immediate rotation of the animal, while in 
the former and quite as unnatural position they hold the animal in persistent stasis— 
this fact tends to show that the righting movements of the pedicels are something 
more than serial. Thus the whole question as between the two hypotheses amounts 
to whether the pedicels are able to act serially from oral to ab-oral pole. Observation 
has shown us that they are so, for we have seen Echini spontaneously rear themselves 
from their normal position on the oral pole, to the position of resting upon their 
equators. Further, as additional evidence that the righting movements are at least 
assisted by some centralizing influence, is the fact that when the evolution is nearly 
completed by the pedicel-rows engaged in executing it, the lower pedicels in the other 
rows become strongly protruded and curved downwards, in anticipation of shortly 
coming into contact with the floor of the tank. 
But, on the other hand, there is evidence to show that the action of the pedicels in 
executing this manoeuvre, although as we have seen in some measure, is not exclusively 
dependent upon this centralizing influence. We found that the centre from which 
this influence proceeds is the nerve-ring that surrounds the lantern. For when this is 
removed, the following results are produced : the pedicels have their spontaneity 
impaired, though not destroyed—the animal still continuing to crawl, but only feebly, 
and no longer in a determinate manner, frequently changing its direction of advance, 
and showing a marked tendency to rotate upon its vertical axis. Moreover, the 
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