NERVOUS SYSTEM OF ANTEDON ROSACEUS. 519 



genus Actinometra is still more remarkable, for here entire arms 

 may be completely devoid of ambulacral groove and epithelium, 

 and of the subepithelial band, and yet such arms, though on 

 Lud wig's theory possessing no nerves at all, are described on 

 Semper's authority as exhibiting as regular and active move- 

 ments while swimming as the other arms. On the other hand, 

 the axial cords or their branches extend along all the arms 

 and pinnules, whether possessing ambulacral grooves or not. 



In all cases the absence of ambulacral grooves is associated 

 with the absence of tentacles. Non-tentaculiferous arms are 

 met with in a large number of species of Actinometra, no less 

 than twenty-three out of the forty-eight species collected by 

 the " Challenger" ^ having more or fewer of such arms, the 

 number of which varies greatly in different individuals. 



In a short paper published in 1883 Perrier^ adopts very defi- 

 nitely the views of the Carpenters concerning the nervous 

 system. He traces branches of the axial cords into connec- 

 tion, through the intermediation of stellate cells, with the 

 muscle fibres. Other branches are traced by him into the 

 tentacles. He gives no figures, however, and his descriptions 

 leave some doubt as to whether the stellate cells do not rather 

 belong to the connective-tissue investment of the nerve or 

 muscle than to the nerves themselves. 



P. H. Carpenter^ has recently described tripolar cells inter- 

 calated in the course of the axial cords and their branches in 

 Antedon. He has also traced in three species of Antedon a 

 fibrillar plexus derived from the axial cords into the connec- 

 tive tissue of the perisome forming the ventral surface of the 

 disc, and is '' strongly inclined to believe that extensions of 

 this plexus are in direct connection with the fibrils of the sub- 

 epithelial bands." 



^ P. H. Carpenter, " Preliminary Report upon the Comatulee of the 

 ' Challenger' Expedition," ' Proceedings of the Royal Society,' No. 194, 1879, 

 p. 395. 



- Perrier, "Note sur Torganisatioa des Criaoides," ' Comptes rendus,' 

 tome xcvii, 1883, pp. 187—189. 



^ P. H. Carpenter, " Notes on Echinoderm Morphology," No. 6 ' Quarterly 

 Journal of Microscopical Science,' 1883. 



