270 PROFESSOR MARSHALL. 



and its prolongations and the arms. A needle was then passed down 

 the canal surrounded by the First Eadials (cf. fig. 1) so as to irritate 

 the chambered organ. "All the ten arms then suddenly and con- 

 sentaneously closed up. On the withdrawal of the needle the arms 

 gradually straightened themselves again, and again coiled up as before 

 when the irritation of the central organ was renewed." 



In January, 1876, Greef 1 called attention to the thickened epithelium 

 forming the floor of the ambulacral grooves both of the arms and disc. 

 He pointed out the close correspondence both in position and histo- 

 logical structure between this ambulacral epithelium of Antedon, and 

 the radial nerves and circumoral commissure of a Starfish, and suggested 

 that the former, like the latter, was nervous in function. At the same 

 time he denied the nervous character of the axial cords. 



In the following month Ludwig, 2 without being acquainted with 

 Greef's work, described for the first time a "delicate fibrillar band " 

 immediately beneath the ambulacral epithelium, i.e. what we have 

 named above the subepithelial band (fig. 2, h), which he regarded on 

 histological and morphological grounds as the true nervous system of 

 Antedon, and as the representative of the radial nerves of other 

 Echinoderms. 



In April of the same year P. H. Carpenter 3 confirmed Ludwig's 

 description of the subepithelial bands which he had himself inde- 

 pendently discovered, and agreed with him in regarding them as 

 nervous. He also showed that the cord x, described by Semper, was 

 not identical as he had supposed with Perrier's fibrous cord, and that 

 neither of these structures corresponded to the subepithelial band, 

 Semper's cord being merely a pigmented cellular thickening between 

 the ambulacral and subtentacular canals, while Perrier's fibrous cord 

 is a muscular band in the ventral wall of the ambulacral canal. 

 P. H. Carpenter, however, differed from Ludwig in regarding not only 

 the subepithelial bands, but the axial cords also as nervous, and he 

 was the first to distinctly maintain the existence in Antedon of this 

 double nervous system, in spite of the morphological difficulties in- 

 volved in this view. He brought forward as additional evidence in 

 favour of the nervous character of the axial cords the fact that in the 



1 Greef, "Ueber den Bau der Crinoideen," 'Sitzungsb. d. Gesellsch. z. Beford. der gesam. 

 Naturwiss. zu Marburg,' No. 1, 1876, pp. 16—29. 



a Ludwig, 'Nachrichten v. der Konigl., Gesellschaft der Wissenschaften, und der Univer- 

 sitat zu Gottingen,' No. 5, Feb. 23rd, 1876. 



a P. H. Carpenter, "Remarks on the Anatomy of the Arms of the Crinoids," 'Journal of 

 Anatomy and Physiology,' April, 1876. 



