On the Structure o/*Antedon rosaceus. 183 



lying immediately beneath the tentacular furrow, it seems to me 

 fair to conclude that the supposed " nerve " of Ludwig, if a nerve 

 at all, has no immediate relation to those movements. 



Experiment 3. — I divided, in another lively specimen of Antedon, 

 the soft parts of one of the arms down to the calcareous segment, 

 thereby cutting through the "nerve" of Ludwig. This ought, on 

 his supposition, to paralyze the arm so treated, or at any rate to 

 destroy the consentaneousness between its movements and those 

 of the other arms. But on replacing the specimen in water, all 

 the arms ivorkecl as usual, without the slightest disturbance of 

 regularity. 



Experiment 4. — I then endeavoured to make a corresponding 

 section of my nerve, the " axial cord," by cutting from the dorsal 

 side of the arm, with the blade of a very thin knife, sufficiently 

 deep between the segments to divide that cord without injuring 

 the " nerve " of Ludwig. Having been repeatedly baffled in this 

 endeavour, however, by the throwing-oif of the half-divided arm, 

 I had recourse to another method, the application of nitric acid. 

 Carefully drying with a bit of blottriig-paper the part to be thus 

 burned away, so as to prevent the spreading of the acid, I applied 

 it \^'ith a finely pointed camel-hair pencil, until I had reason to 

 feel sure that it must have reached the axial canal. On replacing 

 the animal in the water, tJiat arm remained rigidly stretched out, 

 while all the other arms worJced as usual. 



Now if these experiments, taken in connexion with the one 

 described in my Paper, which I have again repeated with the 

 same result, are not admitted as valid evidence that the quin- 

 quelocular organ with its radiating cords constitute a Nervous 

 system, I am at a loss to understand what is the superior pro- 

 bative force of the evidence which is universally held to justify 

 the assignment of such functions to the Brain, Spinal Cord, and 

 the white solid cords proceeding from these centres in a Vertebrate 

 animal. And I should feel it necessary to enter a strong protest 

 against the refusal of a similar character to what I hold to be the 

 Nervous system of the Crinoida (if based on no other objection 

 than that its position does not correspond with that of the 

 accredited Nervous system of other Echinodermata), were it not 

 that an investigation which I commenced seven years ago into the 

 structure of the Ophiurida showed that they will probably afford 

 the means of bridging over this difficulty ; for the calcareous 

 segments of their arms, instead of being perforated by a central 

 canal, have a deep notch on their ventral margin, which is some- 

 times almost completed into a canal ; so that there is here an 

 easy passage on the one hand towards the ventral nerve-cord of 

 the Asteroida, on the other towards the central nerve-cord of the 

 Crinoida. Further, it is to be borne in mind that in the early 

 stage of the development of the Pentacrinoid larva of Antedon, as 

 described in the First Part of my Memoir (Phil. Trans. 1855), 

 the " axial cords " He on the ventral surface of the Eadials and 

 Brachials, which are then mere flat plates ; by an endogenous 



