10 



Mr. G. J. Romanes and Prof. J. C. Ewart. [Mar. 24, 



either direction, it would follow that the persistency with which the 

 partly shaved Echini continue reared upon their equators, is the ex- 

 pression of some stimulus (such as a sense of gravity) continuously 

 acting upon some central apparatus, and impelling the latter to a con- 

 tinuous, though fruitless, endeavour to co-ordinate the absent pedicels. 

 If the pedicels are able to act serially in either direction, there is no 

 more reason why a partly shaved Echinus should remain permanently 

 reared upon its equator, than that it should remain permanently 

 inverted upon its pole ; and therefore the fact that in the latter 

 position the pedicels set about an immediate rotation of the animal, 

 while in the former, and quite as unnatural position, they hold the 

 animal in persistent stasis — this fact tends to show that the righting 

 movements of the pedicels are something more than serial. Thus the 

 whole question as between the two hypotheses amounts to whether 

 the pedicels are able to act serially from oral to aboral pole. Observa- 

 tion has shoAvn us that they are so, for we have seen Echini spon- 

 taneously rear themselves from their normal position on the oral pole, 

 to the position of resting upon their equators. Further, as additional 

 evidence that the righting movements are at least assisted by some 

 centralising influence, is the fact that when the evolution is nearly 

 completed by the pedicel-rows engaged in executing it, the lower 

 pedicels in the other rows become strongly protruded and curved 

 downwards, in anticipation of shortly coming into contact with the 

 floor of the tank. 



But, on the other hand, there is evidence to show that the action of 

 the pedicels in executing this manoeuvre, although, as we have seen, in 

 some measure, is not exclusively dependent upon this centralising 

 influence ; and we found that the centre from which this influence pro- 

 ceeds is the nerve-ring that surrounds the lantern. . For when this is 

 removed, the following results are produced. The pedicels have their 

 spontaneity impaired, though not destroyed — the animal still continuing 

 to crawl, but only feebly, and no longer in a determinate manner, 

 frequently changing its direction of advance, and showing a marked 

 tendency to rotate upon its vertical axis. Moreover the echinus is 

 now no longer able to escape from injury, but when stimulated crawls 

 indifferently in any direction. Thus, removal of the nerve-centre 

 seriously impairs the activity of the pedicles, and totally destroys their 

 co-ordination. Yet when specimens so mutilated are inverted, one out 

 of every four specimens is able to right itself. This, however, is only 

 done with much difficulty and after a long time, so that, under these 

 circumstances, the execution of this manoeuvre seems to be just barely 

 possible. Still the fact of its being possible at all proves that the 

 integrity of the nerve-centre is not absolutely essential to its perform- 

 ance. Therefore, as experiment has failed to reveal to us any other 

 general nerve-centre in the animal, and as even a segment of the 



