288 PROFESSOR MARSHALL. 



As the radial cord (fig. 3) divides into the two axial cords before 

 entering the Third Radial, the sole anatomical connection between the 

 axial cords of the two arms in the above experiment is afforded by the 

 transverse commissure and the chiasma, one or other of which, or 

 both, must therefore furnish the physiological connection which the 

 experiment proves to exist. From the anatomical relations of the 

 parts, and from the fact that the proximal ends of the chiasma must 

 almost certainly have been injured in the operation, I think it probable 

 that the transverse commissure is the real connecting link in this 

 instance. As to the chiasma, the disposition of the fibres suggests 

 that it may be connected with the alternating movements of the two 

 arms of each pair which we have seen to occur in the act of swimming. 



F. On the Functions of the Subepithelial Bands, 

 The subepithelial bands are supposed by Ludwig, as we have seen 

 above, to constitute the sole or main nervous system of Antedon. 

 The experiments detailed above demonstrate the incorrectness of this 

 view. They show that the central connection of the subepithelial 

 bands on the oral disc is in no way essential to, in fact, has nothing- 

 whatever to do with the complicated and co-ordinated movements of 

 swimming, and of righting when inverted ; they show, further, that 

 division or destruction of the subepithelial band at any place does 

 not destroy or even disturb either the sensory or motor communications 

 between the parts on either side of the injury. In fact, they not only 

 prove conclusively that these structures are not the sole nervous 

 system, but even raise doubts as to whether they belong to the system 

 at all. 



I think, however, that the close histological resemblance between 

 the subepithelial bands and the axial cords, coupled with the close 

 correspondence as regards their relations to the ambulacral epithelium 

 which exists between Crinoids and other Echinodermata in which, as 

 in Asterids, they are most certainly nervous, must compel us to con- 

 sider these bands in Antedon as nervous in nature, though what their 

 exact function is has yet to be determined. The ambulacral epithelium 

 is extremely and exceptionally sensitive, and irritation of it is responded 

 to in a definite and peculiar manner, i.e. by the sudden folding of the 

 pinnules alongside the irritated spot. The ambulacral grooves are 

 structures of great importance to the animal, for it is by them that 

 food particles are captured and swept along by the ciliary currents 



