862 
MR, G. J. ROMANES AND PROFESSOR J. C. EWART 
then well rubbed with sandpaper and brickdust.* The spines along these lines were 
laid in a very marked way, while spontaneity and reflex irritability, not only along 
them, but also in the inter-ambulacrcd spaces between them, were completely destroyed. 
The rest of the hemisphere was normally active. 
“ Ten minutes after operation the laid spines became more erect, and reflex irritability 
partly returned. 
“ Twenty minutes after operation pedicellarise nearly completely recovered spon¬ 
taneity and reflex irritability ; spines still very imperfectly so. 
“ Two hours after operation both spines and pedicellarise of the inter-ambulacral 
area completely recovered in cdl respects.” 
(C.) If an Echinus is divided into two hemispheres by an incision carried from pole 
to pole through any meridian, the two hemispheres will live for days, crawling about 
in the same manner as entire animals; if their ocular plates are not injured, they seek 
the light, and wdren inverted they right themselves. The same observations apply to 
smaller segments, and even to single detached rows of ambulacral feet. The latter are, 
of course, analogous to the single detached rays of a Star-fish, so far as the system of 
ambulacral feet is concerned; but looking to the more complicated apparatus of locomo¬ 
tion (spines and pedicellarise), as well as to the rigid consistence and awkward shape of 
the segment—standing erect, instead of lying flat—the appearance presented by such a 
segment in locomotion is much more curious, if not surprising, than that presented by 
the analogous part of a Star-fish under similar circumstances. It is still more sur¬ 
prising that such a fifth-part segment of an Echinus will, when propped up on its 
ab-oral pole (Plate 84, fig. 30), right itself (Plate 84, fig. 31) after the manner of 
larger segments or entire animals. They, however, experience more difficulty in 
doing so, and very often, or indeed generally, fail to complete the manoeuvre. 
(D.) We are now again face to face with a question already propounded in § II., 
viz.: Is the action of the ambulacral feet in executing these righting movements of a 
merely serial kind, or does it depend upon nervous co-ordination? We have found 
this question very difficult of solution, and in the end have arrived at the conclusion 
that both principles are combined-—the action of the feet being serial, but also assisted 
by nervous co-ordination. The experiments which lead us to this conclusion are as 
follows :— 
If an unmutilated Echinus be suspended by a thread in an inverted position half¬ 
way up the side of a tank, in such a way that the ambulacral feet on one side of the 
ab-oral pole are alone able to reach the perpendicular wall, these feet as quickly as 
they can establish their attachments to that wall; the thread being then removed, 
* This method of destroying the hypothetical plexus was here adopted in preference to the method of 
painting with acid, in order to avoid a possible source of fallacy in some of the acid passing through the 
perforations of the shell, and so finding its way over the external surface. All our experiments with acid 
were on other specimens controlled by similar experiments conducted on this method. 
