ON THE LOCOMOTOR SYSTEM OP ECHINODERMATA. 
845 
i.e., they would repeatedly choose the same feet-rows wherewith to execute their 
righting movements. In these individual specimens, therefore, the probability is that 
the feet-rows thus selected were selected because of some slight accidental prepotency 
or superiority over the others; and thus the explanation in all cases doubtless is that, 
although the physiological conditions are pretty nicely balanced, they are not so nicely 
balanced as to leave positively nothing to determine which rows of feet shall be used. 
Another question of still more interest is that as to the prompting cause of all these 
laborious movements. Is it that the animal has some dim consciousness of discomfort, 
owing to a disturbance of a nascent sense of gravity ? Or is the whole series of move¬ 
ments purely mechanical, and determined only by the fact that the feet in the feet- 
rows are all arranged serially, and therefore when feet A, B, and C have established a 
firm hold and thereby tilted the globe over a certain distance, opportunity is afforded 
for D, E, and F to establish a hold, and so on ? This question had better, for the 
present, be deferred. 
(B.) Spines. —(C.) Lantern. —It is, of course, well known that the spines of the 
Echinus are used in locomotion ; but hitherto their action does not seem to have been 
carefully observed, and we are not aware that the part played by the lantern has ever 
been observed at all. Observations on these points may best be made by taking the 
animal out of the water, and placing it upon a table ; it will then soon begin to walk 
in some definite direction— i.e., in a straight line—and in doing so the only organs 
used for the purposes of locomotion are the spines and the lantern, the ambulacral 
feet under these circumstances not being protruded at all. The rate of locomotion is 
very slow, viz., about 1 inch per minute ; but it is continuous, takes place, as already 
observed, in a definite direction, and is accomplished by means of a number of highly 
co-ordinated movements. The latter are as follows :— 
The whole dental apparatus, or lantern, admits of being protruded and retracted; 
when protruded, the sharp and polished point which is composed by the mutual 
contact of the five teeth, stands out below the ventral surface of the animal; when 
retracted, this point is drawn within the body cavity of the animal. The movements 
of protrusion and retraction are perfectly rythmical, at the rate of three or four 
revolutions per minute. When the lantern is drawn back to its fullest extent, it is 
tilted to one side, in such a way that the teeth point towards the direction of advance. 
The lantern is then brought down and protruded till the teeth rest upon the table; 
some of the spines have meanwhile been rotating on their ball and socket-joints, in 
such a way that their points are in a position on the table to push the animal towards 
the direction in which the teeth are pointing. This push being communicated by the 
spines while the teeth are held firmly down, the result is to raise the whole animal 
upon the point of its teeth, and to let it fall again upon the other side of the teeth ; 
the point of the teeth is thus used as a fulcrum, over which the animal is made to 
move by the co-ordinated action of its spines. Of course, when it has completed this 
movement, the teeth are pointing away from the direction of advance—the whole 
