8(56 
MR. G. J. ROMANES AND PROFESSOR J. C. EWART 
is needless to say, the feet of the uninjured rows had to be used serially in the direc¬ 
tion opposite to that in which they are required to act when executing the ordinary 
righting manoeuvre. We may wonder wliat the stimulus can have been which induced 
this Echinus spontaneously to rise upon its equator; but it is of interest in this con¬ 
nexion to add that, so soon as the equator position had been attained, and so soon 
therefore as any further action of the uninjured feet-rows in the same direction would 
have begun to get the animal into a position of ever-increasing difficulty as regards 
subsequent righting, so soon did the serial action in this direction cease, became 
reversed, and so again brought the animal gently into its normal position. 
We have also seen wholly uninjured specimens when reaching the surface of the 
water by crawling up the sides of a tank, spontaneously rear themselves upon their 
equators and remain in that position for several minutes ; but we have never observed 
a case of such rotation carried further than the equatorial line. The fact, however, 
that such rotation from oral to ab-oral pole can take place over half the whole length 
of a pair of feet-rows, proves that the feet may act serially in either direction. The 
same thing is further proved by the fact that single detached rays of Star-fish some¬ 
times crawl backwards, and that in entire Star-fish the rays opposite to the direction 
of advance work their ambulacral feet centripetally, while those on the rays facing 
that direction work centrifugally. 
Lastly, as proof that the ambulacral feet of Echinus are under the control of some 
centralising apparatus when executing the righting manoeuvre, we may state one 
other fact. When the righting manoeuvre is nearly completed by the rows engaged in 
executing it, the lower feet in the other rows become strongly protruded and curved 
downwards, in anticipation of shortly coming into contact with the floor of the tank 
when the righting manoeuvre shall have been completed (see Plate 83, fig. 26). This 
fact tends to show that all the ambulacral feet of the animal are, like all the spines, 
held in mutual communication with one another by some centralising mechanism. 
Such, then, is the evidence we have to adduce for the purpose of showing that the 
action of the ambulacral feet is not entirely or only of a serial kind, but is, in part at 
all events, dependent upon some centralising influence by which all the feet, like all 
the spines, are rendered capable of truly co-ordinated action. We have next to adduce 
our evidence to show that the action of the ambulacral feet, although as we have 
seen in some measure, is not exclusively dependent on this centralising influence. 
(E.) In order to show this we must first narrate the experiments whereby we suc¬ 
ceeded in ascertaining the central apparatus, on the integrity of which both the feet 
and the spines depend for their co-ordination. Having obtained the definite evidence 
of co-ordination which has now been fully detailed, we of course sought to localise the 
centre to which this co-ordination is due; and in searching for this centre our thoughts 
naturally turned to the only part of the nervous system wdiere w r e could reasonably 
expect to find it. This part is the central nerve-ring, and, as we had anticipated, 
