268 PROFESSOR MARSHALL. 



of the arms, each having an ambulacral groove, subepithelial band, 

 tentacles, ambulacral, subtentacular, genital and cceliac canals, a 

 branch of the axial cord, &c. ; the genital rachis, however, which is 

 only a slender cord in the arms, dilates in the pinnules to form the 

 genital glands. The proximal or oral iDinmdes, i.e. those borne by the 

 Second Brachials, differ markedly from the others ; they are longer 

 than the rest, and habitually bend inwards, so as to arch over and 

 cover the disc ; they have no tentacles 1 and no ambulacral grooves, 

 the ciliated epithelium of the grooves and the subepithelial bands being 

 both absent f they possess, however, like the other pinnules, branches 

 of the axial cords of the arms. 



II. Historical Sketch. 



I propose, in this section, to notice briefly the principal views that 

 have been advanced concerning the nervous system of Antedon. 



Miiller, 3 in 1841, gave the first account of the genital rachis in the 

 arms of Antedon, but mistook it for the nervous system, and described 

 it as such ; he also mentioned the axial cords, but described them as 

 vessels. 



In 1865 Dr. Carpenter, in his 'Memoir on the Structure, Physiology, 

 and Development of Antedon rosaceus,' corrected Muller's mistake 

 concerning the genital rachis ; and, with regard to the axial cords, 

 stated: 4 "It will be shown, in the second part of this memoir . . . 

 that a system of branching fibres proceeding from the solid cord that 

 traverses the axial canal of each calcareous segment of the rays and 

 arms is traceable on the extremities of the muscular bundles, and 

 reasons will be given for regarding these fibres as probably having the 

 function of nerves, though not exhibiting their characteristic structure." 



In 1872 Bauclelot 3 called attention to the anatomical and histological 

 resemblances between the axial cords of Antedon and the radial nerve- 

 cords of other Echinoderms. He mentioned the pentagonal commissure 

 in the calyx and the branches of the axial cords to. the pinnules, and 

 described the cords as consisting of fibrils cemented together by a finely 



1 Carpenter, 'Phil. Trans.,' 1886, p. 702. 



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

 'Journal of Anatomy and Physiology,' vol. xi, p. 90. 



3 J. Miiller, "Ueber den Bau des Pentacrinus Caput Medusfe." 'Physikalische Abhandlun- 

 gen der Koniglichen Akademie des Wissenschaften zu Berlin.' 



1 Carpenter, 'Phil. Trans.,' vol. 156, 1866, p. 705. 



6 Baudelot, "Etudes Generates sur le Systeme Nerveux," 'Archives de Zoologie Expiri* 

 mentale,'tome 1, 1872, p. 211, 



