1884.] On the Nervous System of the Crinoidea. 69 



bv means of thin sections the statement I had made ten years pre- 

 yiously, as to the regular transmission of pairs of branches (fig. 1, nm, 

 ?) from the axial cord of the arms to their successive pairs of flexor 

 muscles ; and I adduced what seemed to me conclusive experimental 

 proof that these cords, which radiate from the wall of the central 

 quinquelocular organ, and are further connected with each other by 

 a commissural ring, have a motor function. 



In the first place, I argued that the extraordinary co-ordination 

 which is manifested in the active swimming action of Antedon, when it 

 spontaneously leaves, or is detached from, the anchorage afforded by 

 the grasp of its dorsal cirri, cannot be accounted for without a 

 definite direction from a nervous centre. That this centre is not in 

 a circum-oral ring, is clear from the continuance of the regular move- 

 ments after the complete evisceration of the animal. On the other 

 hand, that it is contained within the centro-dorsal basin, was indicated 

 alike by the coiling-up of the arms when the quinquelocnlar organ 

 was irritated, and by the complete paralysis of the flexor muscles 

 which followed the removal of the centro-dorsal basin with its 

 contents. And, further, the destruction of a portion of the axial cord 

 of an arm, the ventral nerve being left uninjured, was shown to be 

 followed by complete paralysis of the muscles of that arm beyond the 

 injured part. 



The anatomical and the experimental evidence that the quinque- 

 locular organ, with its radiating and branching cords, constitute the 

 motor nervous system of the arms, being thus in complete harmony, 

 I ventured (p. 454) to profess myself " at a loss to understand what 

 is the superior probative force of the evidence which is universally 

 held to justify the assignment of such functions to the brain and 

 spinal cord, and the white solid cords proceeding from these centres, 

 in a Vertebrate animal." 



That the sub-ambulacral band of Ludwig is also a nerve (as 

 homology would indicate), I thought not improbable ; but looking to 

 its immediate proximity to the sensory (ventral) surface, and to the 

 absence of any connexion with the muscular apparatus, I thought 

 that it might probably be an afferent nerve, " the functions of the 

 single trunk of the Asterida being here divided between two, an 

 afferent and a motor, just as, in Man, the double function of an 

 ordinary spinal nerve is divided in the head between the fifth and 

 seventh pairs." 



During the eight years which have elapsed since these statements 

 were made public, it might have been expected that my conclusions 

 would have been either accepted or controverted. But the question 

 has been considered by many eminent Zoologists, especially in 

 Germany, as one which is so conclusively settled by Homology, as not 



