118 THE VOYAGE OF H.M.S. CHALLENGER. 
been acquainted with these facts, the non-nervous nature of the axial cords would 
probably have been somewhat less “ evident” to him. 
According to Ludwig the axial cords consist of “feinen Fasern, zwischen welchen 
man, namentlich an der Peripherie der ganzen Masse, Zellen oder doch zellenihnliche 
Gebilde (Zellkerne ?) findet.”* As a matter of fact I can find no difference between the 
appearance of the fibrils forming the axial cords and those of the ambulacral nerve, 
either in transverse or in longitudinal section ; and I wonder that Ludwig was not struck 
by the resemblance of the two, especially in Antedon eschrichti, in some specimens of 
which, at any rate, it is very marked. There are the same delicate fibrils with inter- 
calated cells as in the ambulacral nerve, and in some individuals the two have exactly 
the same appearance in cross-section; though the axial cords more usually are some- 
what of a yellowish tinge, which renders it easy to recognise their branches that extend 
outwards from the skeleton into the connective tissue of the general perisome (figs. 4-8 ; 
PL V Ub sdigs. 6, 7 3 PL LIX? figs 2=4; 6, 7; Pl. GX. figs. '2; 6). 
Dr. Carpenter’s theory of the nervous nature of the axial cords of the arm was 
originally suggested by his discovery that they give off branches which extend over the 
ends of the muscular bundles. This is well seen in moderately thick transverse sections 
of an arm which are viewed as opaque objects. But the study of thin transparent 
sections shows that these branches to the muscles are only portions of a largely developed 
network which originates in the axial cords and extends both to the dorsal and to the 
ventral surface of the arm or pinnule. Ludwig states that he had been unable to 
convince himself of the existence of the muscular branches described by Dr. Carpenter. 
This may well have been the case in the small arms of Antedon rosacea; though I have 
had no difficulty in finding them in this species, and Perrier has been equally successful. 
But I cannot comprehend his not having seen some of these lateral extensions of the 
axial cords in the arms and pinnules of Antedon eschrichti. They are not limited to the 
skeleton, for I have hardly a section that does not show a part of one or other of the two 
main trunks which extend up into the ventral perisome at the sides of the food-groove, 
as represented in Pl. LX. fig. 6, a’. Pinnule sections too may be obtained without 
difficulty, in which the whole course of one of these branches may be seen from its origin 
in the axial cord right up into the substance of one of the respiratory leaflets bordering 
the food-groove. In Ludwig’s figures of sections through the arms and pinnules, 
however, the axial cord is represented as a mere dark circle without any trace of lateral 
extensions. 
The doctrine of the nervous nature of these cords has recently received support from 
a quarter in which it was formerly denied; for Prof. Perrier has reinvestigated the 
subject and has brought forward additional evidence of much value. He has seen the 
branches of the axial cords in Antedon rosacea, and states, like Baudelot and Teuscher, 
1 Crinoideen, Joc. cit., p. 316. 
