466 THE ORIGIN OF VERTEBRATES 



proved very difficult for physiologists to accept, but also Graham 

 Kerr, in his latest papers on the development of Lepidosiren, has 

 shown that there is continuity between the nerve-cell and the muscle- 

 cell from the very first separation of the two sets of elements ; in 

 fact, Hensen is right and His wrong in their respective interpretation 

 of the earliest stages of the connection between muscle and nerve. 

 So also, it seems to me, the intimate connection between the meta- 

 bolism of the gland-cell, as seen in the submaxillary gland, and the 

 integrity of its nervous connection implies that the connection 

 between nerve-cell and gland-cell is of the same order as that between 

 nerve-cell and muscle-cell. Graham Kerr also states in his paper 

 that from the very commencement there is, he believes, continuity 

 between nerve-cell and epithelial cell, but so far he has not obtained 

 sufficiently clear evidence to enable him to speak positively on this 

 point. 



Further, according to the researches of Anderson, the cells of the 

 superior cervical ganglion in a new-born animal will continue to 

 grow healthily as long as they remain connected with the periphery, 

 even though entirely separated from the central nervous system by 

 section of the cervical sympathetic nerve, and conversely, when 

 separated from the periphery, will atrophy, even though still con- 

 nected with the central nervous system. So, also, on the sensory 

 side, Anderson has shown that the ganglion-cells of the posterior 

 root-ganglion will grow and remain healthy after separation of the 

 posterior roots in a new-born animal, but will atrophy if the peripheral 

 nerve is cut, even though they are still in connection with the central 

 nervous system. Further, although section of a posterior root in the 

 new-born animal does not affect the development of the nerve-cells 

 in the spinal ganglion, and of the nerve-fibres connecting the 

 posterior root-ganglion with the periphery, it does hinder the 

 development of that part of the posterior root connected with 

 the spinal ganglion. 



These experiments of Anderson are of enormous importance, and 

 force us, it seems to me, to the same conclusion as that to which he 

 has already arrived. His words are (p. 511): "I suggest, therefore, 

 that the section of peripheral nerves checked the development of 

 motor and sensory neurones, not because it blocked the passage of 

 efferent impulses in the first case and the reception of stimuli from 

 the periphery in the second, but for the same reason in both cases, 



