STAR- FISH AND SEA-UllCHINS. 313 



probaMy ineluces some degree of shock in the 

 remaining half, and so leaves the corresponding 

 parts of the unmutilated rows prepotent over the 

 mutilated one. Be tliis 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 

 manoeuvre 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 



