ON THE LOCOMOTOR SYSTEM OF ECHINODERMATA. 
837 
ing point, it is needless to dwell upon the well-known mechanism of the ambulacral 
system. The rate of crawling upon a flat horizontal surface is 2 inches per minute. 
The animal usually crawls in a determinate direction, and, while crawling, the ambu¬ 
lacra! feet at the end of each ray are protruded forwards as feelers; this is particularly 
the case with the terminal feet on the ray, or rays, facing the direction of advance. 
When in the course of their advance these tentacular feet happen to come into contact 
with a solid body, the animal may either continue its direction of advance unchanged, 
or may deflect that direction towards the solid body. Thus, for instance, if, while the 
Star-fish is advancing along the floor of a tank, the tentacular feet at the end of one 
of its rays happen to touch a perpendicular side of the tank, the animal may either at 
once proceed to ascend this perpendicular side, or it may continue to progress along 
the floor—feeling the perpendicular side with the ends of its rays perhaps the whole 
way round the tank, and yet not choosing,* as it were, to ascend. What it is that 
determines the animal in some cases to ascend, and in other cases not, we were unable 
to ascertain. 
When a Star-fish ascends the perpendicular side of a tank or bell-jar till it reaches 
the surface of the water, it very frequently performs a number of peculiar movements, 
which we may call acrobatic (see Plate 81, fig. 19). On reaching the surface of the 
water, the animal does not wish to leave its native element, and neither does it wish 
again to descend into the levels from which it has just ascended. It therefore begins 
to crawl to one side or the other, and while crawling it every now and then throws 
back its uppermost ray, or rays, to feel for any solid support that may happen to be 
within reach. The distance to which the rays may thus be thrown back is remarkable; 
for the animal may hold on with its two lower rays alone, or even with the end of a 
single ray, and throw back the whole of the other rays with the central disc into a 
* It may be as well to explain that in using such woi’ds as these, we do not, in the present paper, 
attach to them any psychological signification; they are used as merely metaphorical terms which serve 
most briefly, and therefore most conveniently, to express the resultants of those systems of physiological 
stimuli, the composing members of which we were not able to observe. When one Star-fish appears to 
choose to ascend the side of a tank, while another Star-fish, under apparently precisely similar circum¬ 
stances as to stimulation, seems to prefer walking along the floor, we can only suppose that the circum¬ 
stances of stimulation, although apparently similar, are not really so, and therefore that the difference in 
the result is due to some difference in the stimulation. Of course it may be objected to this that the 
same remark applies to cases in which the psychological element unquestionably enters—choice on its 
physiological side being merely the resultant of some unobservable system of stimuli. But without here 
entering on the whole question of the relation between body and mind, it is enough to point out that the 
only evidence we can have of a physiological determination presenting a psychological side, is by observ¬ 
ing that the organism which exhibits the determination is capable of altering it on future occasions, if 
the determination first made is found by individual experience to be injurious. In other words, the 
power of learning by individual experience is the only unequivocal evidence we can possess of the pre¬ 
sence, in any animal, of a psychological element; and as we have observed no such evidence in the case 
of any of the Echinoderms, we desire it to be understood that we consider all their movements to be of 
the so-called “reflex” kind. 
