272 PROFESSOR MARSHALL, 



that the subepithelial band, if a nerve at all, has no immediate relation 

 to the swimming movements of the arms. 



In 1877 Ludwig 1 published a more detailed account of the subepi- 

 thelial band in Antedon, in which he describes the band and the 

 columnar epithelium covering it as being sometimes directly continuous 

 with one another and sometimes separated by a delicate horizontal 

 lamella. This lamella he finds to be a more constant and evident 

 structure in Antedon Eschrichtii than in A. rosaceus. He considers 

 that the subepithelial band is alone to be regarded as the nerve, and 

 points out that the close histological similarity between this band in 

 Crinoids and the radial nerve of an Asterid, which latter, from the 

 position of the eyes, must certainly be nervous, is a strong argument 

 in support of his view. He also discusses the claim of the axial cords 

 to rank as parts of the nervous system ; but, while admitting the great 

 importance of Dr. Carpenter's experiments, considers that the case is 

 not yet satisfactorily proved, and that the morphological difficulties 

 involved in the possession by Crinoids of a nervous system altogether 

 unknown in other Echinoderms, are too great to permit the acceptance 

 of Dr. Carpenter's views. According to Ludwig, the axial cords are 

 parts of the connective tissue basis of the skeleton, which persist in 

 an uncalcified condition, and are probably nutritive in function. 



P. H. Carpenter, in a further paper on the arms of Crinoids, 2 and 

 in a monograph on the genus Actinometra, 3 brings forward strong 

 additional evidence in support of the nervous nature of the axial cords. 

 He shows that in Antedon rosaceus the oral pinnules differ from the 

 other pinnules, not only in being destitute of tentacles (as pointed out 

 by Dr. Carpenter in 1865), but also in having no ambulacral groove, 

 no thickened ambulacral epithelium, and no trace of the subepithelial 

 band, i.e. that they are totally devoid of what Ludwig considers to be 

 the sole nervous system of Antedon ; and yet these oral pinnules are 

 peculiarly irritable, a slight touch being sufficient to cause all ten arms 

 to be suddenly coiled up over the disc. 



He further finds that in Antedon Eschrichtii this absence of 

 ambulacral groove and epithelium, and of the subepithelial band, occurs 

 not only in the oral pinnules, but at the distal extremities of the 



1 Ludwig, 'Morphologische Sfcudien an Echinodermen,' Heft i, Abh. i; 'Separat. Abdruck 

 aus der Zeitschrift f. wissenschaftliche Zoologie,' Bd. 28. 



2 P. H. Carpenter, "Remarks on the Anatomy of the Arms of the Crinoids," part ii, 

 ' Journal of Anatomy and Physiology,' vol. xi, October 1876. 



3 P. H. Carpenter, " On the Genus Actinometra," 'Transactions of the Linnean Society,' 

 2nd series Zoology, vol. ii, part i, 1879. 



