MR. P. H. CARPENTER ON THE GENUS ACTINOMETRA. 33 



in position and histological structure with the typical Echinoderm nerves. At the same 

 time he denied the nervous nature of both the structures described as nerves by Miiller 

 and Dr. Carpenter respectively, viz. the genital cord, the so-called " rachis," on the one 

 hand, and the axial cords in the centre of the calcareous segments on the other. 



A week after the publication of Green's views, Dr. Carpenter 1 announced his belief 

 that a complicated apparatus, " consisting of the outer cylinder of the Crinoidal stem, of 

 the five-chambered central organ formed by the dilatation of that axis within the centro- 

 dorsal basin, and of the cords proceeding from it to the arms and eirrhi," should be 

 regarded as the central portion of a nervous system. This view was based both upon 

 anatomical and upon physiological considerations : — 



(a) That while a siugle arm may be made to coil up by irritating one of its pinnules, 

 the whole circlet of arms closes together when an irritation is applied to the pinnules, 

 which arch over the mouth — an act which affords a strong indication of the "inter- 

 nuncial" action of a definite nervous system. 



(b) That stimulation of the central quinquelocular organ ("heart" of Miiller and 

 Grceff) contained in the calyx, with which the axial cords of the arms are in connexion, 

 is followed by sudden and simultaneous flexion of all the arms. 



(c) That these axial cords give off successive pairs of branches, which ramify upon the 

 muscles connecting the arm-segments. 



Shortly after the announcement of these views on the part of Dr. Carpenter, Ludwig 2 

 described a ventral nervous system as existing in Comatula in common with all the 

 other Echinoderms. He attributed a nervous character, not to the whole epithelial floor 

 of the ambulacral grooves, as was done by Greeff, with whose researches he was unac- 

 quainted, but to a fibrillar layer beneath it, and more or less distinctly separated from 

 it. This layer, which was also discovered independently by myself 3 and Teuscher 4 , 

 and was regarded by us both as of a nervous nature, is the " subepithelial band " men- 

 tioned in sect. 22. Ludwig, like Greeff before him, denied the nervous character of the 

 dorsal axial cords of the arms ; Teuscher discussed it as possible, but hesitated to accept 

 it on account of the morphological difficulties involved in such a view. 



Baudelot 5 , who seems to have been unacquainted Avith Dr. Carpenter's earlier state- 

 ments, was apparently struck with the nature of these cords, though he could not regard 

 them as nervous. After describing; their structure and their union in the calvx to form 

 the pentagonal commissure, he adds, "Ainsi done chez les Comatules il existe des parties 

 qui eciclemment rC appartiennent point au systeme nerveux (!), et qui dans leur disposition 

 aussibien que dans leur structure offrent une analogie presque complete avec les cordons 

 nerveux des autres Echinodermes." It must be remembered that Baudelot wrote before 

 the discovery of the so-called " ventral nerve " of Comatula ; but, in any case, I do not 

 quite see the force of his " evidemment." 



1 " On the Structure, Physiology, and Development of Antedon rosacew" Troc. Roy. Soc. no. 160, Jan. 20th, 

 1876, pp. 219-226. 



- Gottingen Nachriehten, no. 5, Feb. 23rd, 1S70, p. 106. 



3 Journ. Anat. Phys. x. p. 578. 



4 " Beitr. z. Anat. der Echinodermen, I. Comatula mediterrawa," Jenais. Zeitseh. B. x. p. 253. 



b " Contribution a l'histoire du systeme nerveux des Echinodermes," Arch, de Zool. Exp. et Gen. i. p. 211. 

 SECOND SERIES. — ZOOLOGY, VOL. II. 5 



