ON THE LOCOMOTOR SYSTEM OF ECHINODERMATA. 
8G7 
experiment revealed unmistakable evidence of this being the centre of which we were 
in search. 
If a circular incision be made all the way round the lantern of an Echinus, at a 
sufficient distance from the lantern to insure that the connexions of the nerve-ring; 
with the rest of the organism shall be severed, the following results are produced :— 
1. Pedicels .—Spontaneity impaired, though not destroyed. They are protruded, 
but not in such numbers or with so much activity as in the unmutilated animal; they, 
how r ever, form their adhesions in the ordinary manner whenever they come into con¬ 
tact with a solid surface, and therefore their function of anchoring the Echinus securely 
remains unimpaired. They also still continue able to crawl, but they do so feebly and 
no longer in a determinate direction ; the animal therefore advances slowly and in a 
very uncertain manner, frequently changing its direction of advance, and manifesting 
a marked tendency to rotate upon its own axis, either without moving from one spot 
or gyrating round and round some one or more centres in a wholly aimless way. The 
animals, however, are still able to climb perpendicular surfaces, though in a most 
uncertain manner. When stimulated strongly the activity of the animal is increased, 
but its power of escaping from the source of injury is completely destroyed; it crawls 
indifferently in any direction—as likely as not towards the source of injury—rotates 
upon its axis, and after crawling some distance in one direction may very likely reverse 
that direction, and so return to the place from which it started. All these movements, 
standing in such marked contrast to those exhibited by unmutilated specimens under 
similar circumstances, prove that the co-ordination of the ambulacra! feet has been 
destroyed. On the other hand, the fact that they continue able to act at all proves 
that their activity is not wholly dependent upon the nerve-centre ; all that the des¬ 
truction of this centre entails is the destruction of their power of co-ordinated action. 
When perfectly fresh and vigorous specimens are inverted, a proportion of about 
three to four remain permanently inverted till they die. As this is never the case 
with perfectly fresh and vigorous specimens when unmutilated, there can be no 
question that destruction of the nerve-centre exerts a profound influence on the action 
of the ambulacra! feet upon which the execution of the righting manoeuvre depends. 
On the other hand, the fact that a certain proportion of individuals continue able to 
execute this manoeuvre after destruction of the nerve-centre-—although they never do 
so without much difficulty and great expenditure of time—proves that the integrity of 
this centre is not absolutely essential to the execution of this manoeuvre. Therefore, 
as experiment has failed to reveal to us any other general nerve-centre in the animal, 
and as even a segment of the animal containing but a single row of feet is in many 
cases able to perform this manoeuvre, we conclude, as previously stated, that the 
action of the feet in performing these righting movements is partly of a serial cha¬ 
racter, although, for reasons mentioned in the two previous paragraphs, we further 
conclude that in the unmutilated animal these movements are largely assisted by the 
co-ordinating influence that emanates from the nervous centre. 
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