STAR-FISH AND SEA-URCHINS. 309 
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 rear- 
ing 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 per- 
form the feat is not more than a healthy Kchinus 
ean expend. But much more frequently the 
Kchinus 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 
(Figs. 59, 60, 61), and suppose that 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 (ze. 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 (ue. 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 ° 
