514 A. MILNES MARSHALL. 



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 granular substance and 

 with very small cells imbedded in the fibrillar tissue. He 

 appears to have been unacquainted with Dr. Carpenter's work, 

 and, in spite of the resemblances he points out so clearly, denies 

 absolutely the nervous nature of the axial cords without stating 

 definitely his reasons for so doing. 



Semper, in 1874^, published an independent refutation of 

 Miiller's error as to the genital rachis, and suggests concerning 

 the nervous system, in ignorance of Dr. Carpenter's statement 

 quoted above, " It might even be possible that the cord in the 

 interior of the calcareous skeleton (i. e. the axial cord) is a 

 nervous cord ; and if so, then the so-called heart situated in 

 the calyx would certainly have to be looked upon as a ganglion." 

 Semper also suggests that a fibrous cord described by Perrier" 

 as lying above, i. e. on the ventral side of the tentacular canal, 

 may also belong to the nervous system. He confirms the 

 existence of this cord, and refers to it as .a^ in a diagrammatic 

 transverse section of an arm. 



In an addendum to the translation of Semper's paper^ and in 

 a second communication to the Royal Society on the structure, 

 physiology, and development of Antedon rosaceus/ Dr. Car- 

 penter further develops the theory that the axial cords " are 

 really nerve-trunks, and that the five-chambered organ in the 

 centrodorsal basin is their centre." He refers to the " quickness 

 and consentaneousness " with which the coiling and uncoiling 

 of the arms are eflFected, and to the fact that irritation of the 

 oral pinnules causes the whole circlet of arras to close together 



1 Semper, " Kurze Anatomische Bemerkungen ueber Comatula," ' Arbeiten 

 aus dem Zoo!, Zoot. Institut in Wiirzburg,' Band i, 1874, p. 259. Translated 

 in the ' Annals and Magazine of Natural History,' 1875, p. 202. 



" Perrier, ' Archives de Zoologie Experimentale,' tome ii, 1873, p. 55. 



^ Carpenter, * Annals and Magazine of Natural History,' 1875, p. 206. 



■• Carpenter, ' Proceedings of the Royal Society,' 1876, p. 226. 



