308 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
seem sufficient to prove the fact of a general co- 
ordination among the feet; but further reflection 
will show that it is not so. For the feet being all 
arranged in regular series, when one row begins to 
effect the rotation of the globe, it may very well be 
that its further rotation in the same direction is due 
only to the fact that the slight tilt produced by the 
pulling of the first feet in the series A, B, C gives 
the next feet in the series D, E, F an opportunity 
of reaching the floor of the tank; their adhesions 
being established, they would tend by their pulling 
to increase still further the tilt of the globe, thus 
giving the next feet in the series an opportunity of 
fastening to the floor of the tank, and so on. In 
order, therefore, to see whether these righting 
movements were due to nervous co-ordination 
among the feet, or merely to the accident of the 
serial arrangement of the feet, we tried the experi- 
ments which I shall now detail. 
First of all we took an Echinus, and by means of 
a thread suspended it upside-down in a tank of 
water half-way up the side of the tank, and in such 
a way that only the feet on one side of the ab-oral 
pole were able to reach the perpendicular wall of 
the tank. These feet as quickly as possible estab- 
lished their adhesions to the perpendicular wall, 
and, the thread being then removed, the Echinus 
was left sticking to the side of the tank in an in- 
verted position by means of the ab-oral ends of two 
adjacent feet-rows (Fig. 59). Under these circum- 
stances, as we should expect from the previous ex- 
periments, the animal sets about righting itself as 
