134 MR. Q. J. ROMANES ON THE 



their adhesions, and so on. Such being the questions to deter- 

 mine, sundry experiments were described, with the result of 

 tending to show that the raanceuvre must at least in part be due 

 to the coordinating influence of a nerve-centre. Mr. Prancis 

 Darwin, having read the account of these experiments, suggested 

 an additional one, v^rhich I have tried, with the result of definitely 

 settling the question. This experiment and its results are as 

 follows : — 



An Echinus is inverted with its aboral pole resting oa the 

 bottom of a large bottle filled to the brim with sea-water. The 

 mouth of the bottle is then corked (no air-bubbles being in- 

 cluded), and placed upon the rotating apparatus which Mr. Darwin 

 and his father used for investigating the geometrism of plants. 

 That is to say, the Echinus was continuously rotated in a vertical 

 plane. I found that so long as the rotation was continued, whether 

 rapidly or slowly, the Ecliinus did not attemj)t to right itself ; 

 but that, when the rotation was allowed to cease, it began to do 

 so after two or three minutes. Moreover, if allowed to do so 

 until it had raised itself into the equatorial, or any other inter- 

 mediate position, and the rotation were then resumed, the 

 position gained was permanently retained so long as the rotation 

 was continued. Therefore I could entertain no doubt that the 

 effect of the rotation was that of confusing, as it were, the coor- 

 dinating influence of a nerve-centre, the stimulus to the operation 

 of which, in the absence of rotation, is gravity. As shown in the 

 Royal Society paper, this nerve-centre is in part, though not 

 exclusively, the circumoral ring. 



Thinking it might be worth while to try the effect of very 

 rapid rotation upon the coordinating power of this nerve-centre, 

 1 tied the bottle containing the Echinus to the spokes of a cart- 

 wheel, which was tilted off the ground to admit of free rotation. 

 By means of a long rope coiled round the axle, and then 

 uncoiled as rapidly as possible by my running away with the free 

 end of the rope, the Echinus was submitted to exceedingly rapid 

 rotation for two or three minutes at a time ; but I could not see 

 that, on being suddenly brought to rest, the functions of the 

 nerve-centres w^ere in any degree impaired. 



As additional proof that the righting movements are due to a 

 sense of gravity leading to coordinating action of the pedicels, I 

 may mention the fact that if an Echinus is inverted in a circular 

 beaker filled with water and of a size just sufiicient to contain 



