THE NERVOUS SYSTEM OP ANTEDON ROSACEUS. 273 



arms and other pinnules. The allied genus Actinometra is still more 

 remarkable, for here entire arms may be completely devoid of ambu- 

 lacral groove and epithelium, and of the subepithelial band, and yet 

 such arms, though on Ludwig's theory possessing no nerves at all, are 

 described, on Semper's axithority, as exhibiting as regular and active 

 movements 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" 1 having more 

 or fewer of such arms, the number of which varies greatly in different 

 individuals. 



In a short paper published in 1883 Perrier 2 adopts very definitely 

 the views of the Carpenters concerning the nervous system. He traces 

 branches of the axial cords into connection, through the intermediation 

 of stellate cells, with the muscle fibres. Other branches were 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 3 has recently described tripolar cells intercalated 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 connective 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 subepithelial bands." 



Finally, Dr. Carpenter has very recently 4 given a summary of the 

 investigations concerning the nervous system of the Crinoids which 

 have been published since his former paper in 1876. He points out 

 that the evidence accumulated in this interval is most strongly in 



1 P. H. Carpenter, "Preliminary Report upon the Comatulse of the 'Challenger' Ex- 

 pedition," ' Proceedings of the Royal Society,' No. 194, 1879, p. 395. 



s Perrier, " Note sur l'organisation des Crinoides," 'Coinptes rendus,' tome, xcvii, 1883, 

 pp. 187—189. 



3 P. H. Carpenter, "Notes on Echinoderm Morphology," No. 6, 'Quarterly Journal of 

 Microscopical Science,' 1883. 



1 Carpenter, "On the Nervous System of the Crinoidea," 'Proceedings of the Royal 

 Society, ' 1884. 



