20 Proceedings of the Royal Physical Society. 



In Fig. 6, I show a diagrammatic transverse section through the body 

 of such a hypothetical ancestral vertebrate with ccelenteric pouches and proto- 

 stoma, and the point which I wish to bring out is that in such forms the part 

 of the endoderm, which later forms the tip of the ccelenteric pouch, would be 

 at first joined up to the central nervous system by a continuous and com- 

 paratively short extent of epithelium with its underlying nerve plexus. The 

 motor nerve trunks of existing Vertebrates would represent localised thicken- 

 ings of this plexus passing from central nervous system to each ccelenteric 

 pouch. Here I am perhaps wandering into the realms of very " high 

 morphology." I have ventured to do so because it has been urged to me by 

 various friends, that there must have been originally a free growth outwards 

 of nerve trunks from the primitive central nervous system to the myotomes 

 which they supply. 



{Issued separately, 17th February 1910.) 



