70 Dr. W. B. Carpenter. [May 29, 



to be a matter for discussion ; it being impossible (in their judgment) 

 that the axial cords of the arms should be nerves, whatever may be 

 the anatomical and experimental evidence that they are. I would 

 submit, however, that the possibilities of Nature are not limited by 

 the dicta of her interpreters;* that anatomical and experimental 

 facts are not to be set aside by preconceived theoretical opinions ; 

 and that the morphology of the Crinoidea has to be settled upon the 

 basis of their own organisation, before it is brought into comparison 

 with that of other Echinodermata. Now the question whether the 

 axial cords of Crinoidea do, or do not, form part of their nervous 

 system, has to be decided: first, by their Histological character; 

 secondly, by their Anatomical distribution ; and, thirdly, by Physio- 

 logical evidence ; and on each of these points I have now a 

 large body of new evidence to adduce, derived from the careful and 

 minute investigations on which my son, Dr. P. Herbert Carpenter, has 

 been continuously engaged during the last eight years. Of the results 

 of these investigations, which are scattered through the various 

 papers he has published on " Crinoid Morphology," I shall now 

 present a summary, arranged under the above heads ; referring to 

 those papersf for a more detailed statement of them. 



Histological Character. Although the axial cords do not consist of 

 tubular nerve-fibres their substance being essentially protoplasmic, 

 and showing but an indistinct fibrillation when hardened in spirit 

 yet, scattered through these cords and their branches, Dr. P. H. 

 Carpenter has found distinct bi-polar and multi-polar cells ; and he 

 has further ascertained that the sub-ambulacral band presents a 

 histological character so precisely identical, notwithstanding the 

 difference of its origin, as to afford a strong presumption that if the 

 latter is a nerve, the former likewise is so. On the other hand, the 

 axial cords, which are regarded by Ludwig as merely unconsolidated 

 portions of the basis-substance of the calcareous segments, differ 

 essentially from that substance histologically. 



Anatomical Distribution. Nothing can be more marked or more 

 constant than the distribution of the branches (fig. 1, nm, nm) of 

 the axial cords to the very definite inter-segmental muscular bundles 

 of the arms and pinnules, alike in the free and in the pedunculate 



Every one familiar with the History of Science knows how often such a priori 

 assumptions have been made and disproved. 



t " Remarks on the Anatomy of the Arms of the Crinoids," in " Journal of 

 Anatomy and Physiology " (1876), vol. x, p. 584, and vol. li, pp. 87-93 ; " On the 

 Genus Actinometra" in " Transactions of Linnaean Society," Second Series, Zool., 

 vol. ii, pp. 32-37 ; " On the Comatula of the ' Challenger ' Expedition," " Proc. 

 Roy. Soc.," March 6, 1879, pp. 394-395 ; " The Minute Anatomy of the Brachiate 

 Echinoderms," in " Quarterly Journal of Microscopical Science," vol. xxi, pp. 

 l'J3, and vol. xxiii, pp. G14-616. 



