446 MR. p. H. CARPENTER ON THE GENUS ACTINOMETRA. 



all the other Echinoderms. This objection has been strongly 

 urged by various German authors, who all assign a nervous cha- 

 racter to the fibrillar subepithelial band above mentioned, since it 

 occupies the same relative position as a very similar structure that 

 has been hitherto generally regarded as representing the nervous 

 system of the Asterids. It e:xtends along the ventral surface of the 

 arms and pinnules beneath the ambulacral grooves, and forms a 

 ring round the mouth beneath the ciliated epithelium of the pe- 

 ristomial area, just above the water-vascular and blood-vascular 

 rings. This band was discovered independently and nearly si- 

 multaneously by the author and by three G-erman observers, all 

 of whom regard it as representing the nervous system of Gomatula, 

 and deny the nervous nature of the axial cords. Dr. Carpenter's 

 experiments at Naples*, however, have fully proved that the co- 

 ordinated swimming-movements of the arms are entirely inde- 

 pendent of this subepithelial band, and are carried on even when 

 the visceral mass containing the oral ring is entirely removed from 

 the calyx ; so that this structure, if a nerve at all, cannot be re- 

 garded as motor in function. It gives off no branches, except an 

 extremely minute one beneath the epithelium of each respiratory 

 leaf and tentacular group. 



If, however, the axial cords are not nerves, and if these ventral 

 subepithelial bands are to be regarded as the only nervous struc- 

 tures in the whole Crinoid organization, the difficulty presents 

 itself that the oral pinnules of the European Crinoids, and more 

 than half the arms, with the majority of the pinnules of some 

 forms of Actinometra, are entirely devoid of a nervous supply. 



The oral pinnules of Antedon have been shown by Dr. Carpenter 

 to be extremely susceptible of irritation. When they are touched in 

 the living animal, the whole circlet of arms is suddenly and simul- 

 taneously coiled up over the disk, while irritation of one of the ordi- 

 nary pinnules is simply followed by flexion of the arm which bears it. 



The structure of these oral pinnules, which are borne in Antedon 

 rosacea by the second brachials, differs very considerably from that 

 of the pinnules borne by the other brachial segments ; for not only 

 are they sterile, but they have neither tentacular apparatus nor 

 ambulacral groove, their ventral surface being slightly convex, 

 while the ordinary ciliated epithelium of the groove with the sub- 

 jacent subepithelial band, the so-called "ambulacral nerve," are 



* Supplemental Note to a paper "On the Structure, Physiology, and Deve- 

 lopment of Antedo7i rosaceus" Proceedings E. S., No. 169, 1876. 



