118 THE VOYAGE OF H.M.S. CHALLENGER. 



been acquainted v/itli 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 " fciiicn Fasern, zwischen welchen 

 man, namentlich an der Peripherie der ganzen J\Iasse, Zellen odcr doch zellenahnliche 

 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 Antcdon 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 ambulaci'al 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 genei'al jDerisome (figs. 4-8 ; 

 PI. Vllb. figs. 6, 7 ; PI. LIX. figs. 2-4, 6, 7 ; PL LX. 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 ofi" branches which extend over the 

 ends of the muscular bimdles. 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 difiiculty 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 PI. 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, loc. cil., p. 316. 



