12 Proceedings of the Hoyal Physical Society. 



(1) The motor nerve trunk is already present as a protoplasmic bridge 

 placing spinal cord and myotome in organic continuity at a period so 

 early that these two structures are still in immediate contact. It is clear 

 that this fact, and similar observations have been made by Stewart Paton 1 

 on Elasniobranchs, places completely out of court, for these particular cases, 

 the view taught by His of the free outgrowth of nerve fibres. Here a 

 protoplasmic nerve trunk is present long before nerve fibres have made 



Fig. 1. 



Part of transverse section through Lepidosiren larva of stage 24, showing 

 motor nerve trunk (».) in the form of a thin protoplasmic bridge connecting 

 spinal cord (s.c.) and myotome (in.). 



their appearance. Of course there is no proof that the protoplasmic bridge 

 has not itself been formed by outgrowth, but on the other hand there is 

 no justification for assuming that it has been. Observation merely testifies 

 that the connection is there from the very early period mentioned. 



(2) The protoplasmic nerve trunk, at first merely granular, gradually 

 assumes a fibrillated structure. 



1 Mitt. Zool. Sta. Naples, vol. xi., L907, 



