182 Royal Society : — 



consentaneous advancement of the five right and then of the^y« 

 left arms, each of which is bent forwards in a curve which 

 resembles that of the swan's neck in its graceful arch, and is then 

 straightened backwards. The perfect similarity of the movements 

 of all the five arms that work together, involving the conjoint 

 contraction of several hundred pairs of muscles, seems to me to 

 point almost certainly to coordination through a nervous centre ; 

 and it will be seen that experiment has fully confirmed that 

 conclusion. 



It will be recollected that the centre of what I regard as the 

 motor nervous system is the quinqueloeular organ contained in 

 the centro-dorsal basin, which Miiller (who did not recognize its 

 cavitary subdivision) characterized as a heart. Mliller's ^dew of 

 its nature is still upheld by Greef {loc. cit.), who says that it gives 

 off vessels to the cirri, and regards what I have described as a 

 circular commissure (analogous to the " circle of Willis ") as a 

 closed blood- vascular system in connexion with this, although he 

 admits that the axial cords of the arms, which are derived from 

 this ring, are solid. The careful and repeated investigations I 

 have made on this point, however, have fully satisfied me that my 

 previous statement was correct. There is no passage whatever 

 out of the chambers into the axial cords either of the cii'ri or the 

 rays ; and in the pedunculate Crinoids, as in the early Pentacri- 

 noid stage of Antedon, there is no ventricular dilatation, the solid 

 radial cords directly arising from the axis. 



Experiment 1. — Taking up a large and vigorous specimen of 

 Antedon, I turned the entire ^^.sceral mass out of the calyx, leaving 

 behind it, therefore, as the centrum of the animal, only the calca- 

 reous segments of the calyx with their muscles and ligaments, the 

 centro-dorsal basin with its cirri, and the five-chambered organ 

 contained in the cavity of that basin. On replacing the animal in 

 the water, it executed the usucd sivimming movement as perfectly as 

 the entire animal had previously done. 



Experiment 2. — I i-emoved from a second specimen, which I 

 took out of the water in the act of swimming, the entire centro- 

 dorsal basin, with its contents and appendages, leaving every other 

 part as it was. On replacing the animal in the water, all the arms 

 were rigidly straightened out, apparently by the action of the elastic 

 ligaments, which the muscles were powerless to antagonize. 



This second experiment, then, not only confirmed my previous 

 belief that the source of the perfect coordination of the swimming 

 movements lies in a JN'ervous centre, but seemed to establish 

 beyond doubt that the quiuquelocular organ is the instrument of 

 that coordination — the centre of a Nervous system, whose peri- 

 pheral portion consists of the axial cords of the rays, arms, and 

 pinnules. On the other hand, the first experiment, taken in con- 

 nexion with the second, clearly shows that nothing contained in 

 the visceral mass is essential to the perfect coordination of the 

 swimming movements. And since it is clearly in the oral ring 

 that we should expect to find the centre of any nervous system 



