34 ME. p. H. CARPENTER ON THE GENUS ACTIXOMETEA. 



In the centre of every segment of the skeleton of Act. polymorpha and of all the other 

 Comatiila which I have examined, from the first radials to the ends of the arms and 

 pinnules, and also in the cirrhus-segments, these axial cords increase considerably in 

 size, and give off four principal branches. Two of these run towards the ventral side, and 

 in the calyx disappear in the neighbourhood of the muscles connecting the segments, 

 though I must confess that I have never been able to trace them any further (PI. VIII. 

 fie. 3, «'). In the arm-segments, however, they continue their course towards the ventral 

 surface and break up into numerous branches, some of which, as I have already described', 

 extend to the tips of the crescentic leaflets at the sides of the tentacular furrow. The 

 two inferior or dorsal trunks run towards the surface of the skeleton ; and while some 

 of their branches are lost in the plexus of tissue forming its organic basis, others seem to 

 become connected Avith epidermic structures in a manner which will be described at 

 length further on. 



Not one of the German observers makes any mention of these branches, although two 

 of them at least have examined Antedon Eschricldii, while they have all cut sections of the 

 arms of species of Actiriometra, in which genus I find them to be particularly distinct. 

 It is obvious that the facts above stated strongly support the view expressed by Dr. Car- 

 penter and by myself, that the axial cords of the arms are of a nervous nature ; and the 

 experiments made by Dr. Carpenter - at Naples have shown conclusively : — 



1. That the quinquelocular organ is the instrument of the perfect coordination of the 

 swimming movements of the arms, which involve the conjoint contraction of several 

 hundred pairs of muscles. 



2. That nothing contained in the visceral mass is essential to the perfect coordination 

 of the swimming-movements, and that therefore the subepithelial band or ambulacra! 

 nerve of the German authors has no immediate relation to those movements, even if it 

 be a nerve at all. 



3. That section of the subepithelial band in an arm does not prevent its playing its 

 usual part in the regular swimming-movements. 



4. That destruction of the axial cord of an arm by the application of acid causes the 

 arm to become rigidly stretched out, Avhile all the others work as usual. 



Since the publication of these experiments Greeff seems to admit the nervous nature 

 of the axial cords, and of the yellowish fibrillar envelope (PI. VIII. figs. 1-3, N) of the 

 quinquclocular organ from which they proceed. Ludwig '\ however, while allowing 

 their force, cannot admit the existence in the Crinoids of an antiambulacral nervous 

 system, of which wo know as yet no homologuc in the other Echinoderms, but sees 

 no difficulty in regarding the quinquclocular organ, its fibrillar envelope, and the 

 axial cords proceeding from it, as parts of a blood-vascular system, like that of the other 

 Echinoderms, although he admits (p. 87) tliat " ihnen vergleichbare Gebilde sind bis 

 jetzt bei anderen Echinodermen nicht bekaunt gewordcn." The axial cords of the 



' Journ. Auat. Phys. x. p. 5S4. 



- " Supplemental >'oto to a Paper on the Structure, Phj-siol. and Develop, of Antedon rosaaus," Proe. Roy. Soc. 

 no. 169, 1S76. 



' " Bcitr. zur Anat. der Crinoldeen," Sep.-Abdruck aus der Zcitscb. f. wisscnscli. Zool. B. xxviii. Heft 3, p. 81. 



