016 JELLY-FISH; STAR-FJSrr, AND SEA-URCHINS. 



in a vertical plane. The object of this was to 

 ascertain whether the continuous rotation in a 

 vertical plane would prevent the animal from right- 

 ing itseU' (because confusing the nerve-centres 

 which, under ordinary circumstances, could feci by 

 their sense of gravity wliich was up and which 

 was down), or would still allow the animal to right 

 itself (because not interfering with the serial action 

 of the feet). AVell, it was found that this rotation 

 of the whole animal in a vertical plane entirely 

 ])re vented the righting movements during any 

 length of time that it might be continued, and that 

 tiiese movements were immediately resumed as 

 soon as the rotation was allowed to cease. This, 

 moreover, was the case, no matter what phase of 

 the righting manoeuvre the Echinus might have 

 reached at the moment when the I'otation began. 

 Thus, for instance, if the globe were allowed to 

 liave reached the position of resting on its equator 

 befoi-e the rotation was commenced, the Echinus 

 would remain motionless, holding on with its equa- 

 torial feet, so long as the rotation was kept up. 



Therefore, there can be no question that the am- 

 bulacral feet are all under the influence of a co- 

 O'dinating nerve-centre, quite as much as are the 

 spines. But, on the other hand, experiments show 

 that the centre in this case is not of so localized a 

 character as it is in the case of the spines ; for 

 when the nerve-ring is cut out, the co-ordina- 

 tion of the feet, although impaired, is not Avholly 

 destroyed. Take, for instance, the case of the 

 righting manoiuvre. The effect of cutting out the 



