454 On the Structure of Antedon rosaceus. [Apr. 6, 



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 throw- 

 ing-oif of the half -divided arm, I had recourse to another method, the 

 application of nitric acid. Carefully drying with a bit of blotting-paper 

 the part to be thus burned away, so as to prevent the spreading of the 

 acid, I applied it with a finely pointed camel-hair pencil, until I had 

 reason to feel sure that it must have reached the axial canal. On re- 

 placing the animal in the water, that arm remained rigidly stretched out, 

 while all the other arms ivorlced 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 quinquelocular organ with its radia- 

 ting cords constitute a Nervous system, I am at a loss to understand 

 what is the superior probative 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 Ojphiurida 

 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 sometimes 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 " lie 

 on the ventral surface of the Eadials and Brachials, which are then mere 

 fiat plates ; by an endogenous thickening of the calcareous network of 

 those plates, the axial cords come to lie in furrows channelled out in their 

 ventral surfaces; while by a further endogenous growth of that network 

 these ventral furrows are completed into canals; and it is by a still 

 further endogenous thickening that these canals finally come to occupy 

 the centre of each Radial and Brachial calcareous segment. 



At the same time I would repeat that I see no reason for refusing to 

 believe that the subepithelial band of Ludwig is a sensory nerve, the 

 functions of the single trunk of the Asteroida being here divided between 



