STAR-FISH AND SEA-URCHINS. 313 
probably induces some degree of shock in the 
remaining half, and so leaves the corresponding 
parts of the unmutilated rows prepotent over the 
mutilated one. Be this as it may, however, we 
found that the difficulty was easily overcome by 
tilting the animal over upon its mutilated feet-rows 
sufficiently far to prevent the unmutilated rows 
from reaching the floor of the tank. When held 
steadily in this position for a short time, the muti- 
lated rows established their adhesions, and the 
Echinus was then left to itself. Under these cir- 
cumstances an Echinus will always continue the 
manceuvre along the mutilated feet-rows with 
which it was begun, till the globe reaches the posi- 
tion of resting upon its equator, and therefore 
arrives at the line where the shaved area com- 
mences. The animal then remains for hours in this 
position, with a gradual but continuous motion 
backwards, which appears to be due to the suc- 
cessive slipping of the spines—these organs in the 
righting movements being always used as props for 
the ambulacral feet to pull against while rearing 
the globe to its equatorial position, and in perform- 
ing this function on a slate floor the spines are 
liable often to slip. The only other motion ex- 
hibited by Echini thus situated is that of a slow 
rolling movement, now to one side and now to 
another, according to the prepotency of the pull 
exerted by this or that row of ambulacral feet. 
Things continue in this way until the slow back- 
ward movement happens to bring the animal 
against some side of the tank, when the uninjured 
