ON THE LOCOMOTOR SYSTEM OE ECHINODERMATA. 
863 
the Echinus is left sticking to the side of the tank in an inverted position by means 
of the ah-oral ends of two adjacent feet-rows (Plate 85, fig. 32). Under these circum¬ 
stances, as we should expect from the previous experiments, the animal sets about 
righting itself as quickly as possible. Now, if the righting action of the feet were 
entirely and only of a serial character, the righting would require to be performed by 
rearing the animal upwards; the effect of foot after foot in the same rows being 
applied in succession to the side of the tank, would require to be that of rotating the 
globular shell against the side of the tank towards the surface of the water, and 
therefore against the action of gravity. This is sometimes done, which proves that 
the energy required to perform the feat is not more than a healthy Echinus can 
expend. But much more frequently the Echinus adopts another device, and the only 
one by which it is possible for him to attain his purpose without the labour of rotating 
upwards: he rotates laterally and downwards in the form of a spiral. Thus, let us 
call the five feet-rows, 1, 2, 3, 4, and 5 (Plate 85, figs. 33 and 34), and suppose that 
rows 1 and 2 are in use near their ab-oral ends in holding the animal inverted against 
the perpendicular side of a tank. The downward spiral rotation would then be 
effected by gradually releasing the outer feet in row 1, and simultaneously attaching 
the outer feet in row 2 (i.e., those nearest to row 3, and furthest from row 1), as far 
as possible to the outer side of that row. The effect of this is to make the globe roll 
far enough to that side to enable the inner feet of row 3 (i.e., those nearest to row 2), 
when fully protruded, to touch the side of the tank. They establish their adhesions, 
and the residue of feet in row 1, now leaving go their hold, these new adhesions serve 
to roll the globe still further round in the same direction of lateral rotation, and so 
the process proceeds from row to row ; but the globe does not merely roll along in a 
horizontal direction, or at the same level in the water, for each new row that comes 
into action takes care, so to speak, that the feet which it employs shall be those which 
are as far below the level of the feet in the row last employed as their length when 
fully protruded (i.e., their power of touching the tank) renders possible. The rotation 
of the globe thus becomes a double one, lateral and downwards, till the animal assumes 
its normal position with its oral pole against the perpendicular tank wall. So consider¬ 
able is the rotation in the downward direction, that the normal posit!on is generally 
attained before one complete lateral, or equatorial, rotation is completed. 
The result of this experiment, therefore, implies that the righting movements are 
due to something more than the merely successive action of the series of feet to which 
the work of righting the animal may happen to be given. The same conclusion is 
pointed to by the results of the following experiment. 
A number of vigorous Echini were thoroughly shaved with a scalpel over the whole 
half of one hemisphere-— i.e., the half from the equator to the oral pole. They were 
then inverted on their ab-oral poles. The object of the experiment was to see what 
the Echini which were thus deprived of the lower half of three feet-rows would do 
when, in executing their righting manoeuvres, they attained to the equatorial position 
