ON THE LOCOMOTOR SYSTEM OF ECHINODERMATA. 
853 
the co-ordinated action of its spines alone ; and also that an Echinus, when taken out 
of the water and placed upon a table, will walk in a determinate direction by the 
same means. The very complete co-ordination of the spines implied by these facts is, 
however, rendered still more conspicuous by experiments in stimulation ; for if, while 
an Echinus is walking on the table in the manner just alluded to, a scrape with a 
scalpel, a drop of spirit, a lighted match, or any other severe stimulus be applied at 
some one part of the animal’s exterior, the spines all over the surface begin to take on 
an active bristling movement, and the direction of advance is immediately changed 
into a straight line of escape from the source of injury. And, were it necessary, other 
experiments could be detailed to show that the multitudinous spines of an Echinus 
are as closely co-ordinated in their action as so many limbs. To this account of the 
physiology of the spines it may be added that the nervous plexus overlying the 
tubercles on which they are mounted is more sensitive to stimulation than any other 
part of the external plexus. This is shown by the fact that, if the tubercle is stimu¬ 
lated by enclosing the spine in the tube of a pipette, and pressing the tubercle with 
the glass edges of the latter, more activity and a greater extent of irradiation of the 
stimulus among the spines and pedicellariae is observed, than when any other part of 
the surface is similarly stimulated. 
4. Detailed eacts of stimulation. —At the commencement of this section it 
has already been stated, as a general fact, that when two points of the surface of an 
Echinoderm are irritated, the direction of advance which results from their joint 
influence is usually the diagonal between the two; also that, “ when a greater number 
of points are irritated, the direction of advance becomes uncertain;” and lastly, that 
if any, even short interval of time is allowed to elapse between the application of 
successive stimuli to different parts of the surface, the direction of advance will be in 
a straight line away from the stimulus applied latest.” The following more detailed 
observations on this subject may here be worth recording. 
Echini actively crawling in water along the floor of a tank were the subjects of the 
experiments, which are thus recorded in our notes :— 
if 1. Cut off tips of spines facing direction of advance—no effect. 
“2. Cut off tips of protruded feet facing direction of advance—all the rest of the 
row retracted, animal stopped for some minutes, and then proceeded in the 
same direction as before. 
“ 3. Plucked out some pedicellarise facing direction of advance—no effect. 
“ 4. Scraped with a needle small portion of the surface facing direction of advance 
-—animal immediately stopped and reversed its direction. 
Injuries 1, 2, 3, and 4, were inflicted on the equator. 
“ 5. Scraped equator with a scalpel on two points opposite to each other—animal 
crawled at right angles to the line of injury. 
“ 6. Scraped similarly at the aboral pole—no effect; there was no reason why 
injury here should determine escape in one direction rather than in another. 
