198 THE EVOLUTION OF CONTINUITY 



The terminally compressed segments would take the 

 form of a solid tissue mass surrounding the distal part of 

 the digestive tube with its inherited opening. There would 

 be a narrowing of the tube in the compressed region, and 

 at the same time the nerve ganglia of successive compressed 

 segments would develop in close continuity to form a 

 primitive brain. Terminal compression would also probably 

 provide strong thick tentacles representing growth from 

 the several compressed segments forming the head (Fig. 64). 



But all parts of the new type would be evolving in their 



Fig. 64. — Terminal compression in the evolving atypical Fish. 

 The diagram does not, of course, represent an actual stage of 

 evolution, but is merely meant to show how inherited poten- 

 tialities would be affected by pressure in their attempts at 

 realisation. H, the head-region, with narrow oesophagus, o, 

 passing through it. h is composed of several compressed 

 segments, whose successive nerve-ganglia are compressed to 

 form g, the compound ganglion or primitive brain. Below 

 the head is a comparatively uncompressed body with wide 

 digestive tract, drawn as communicating at the convex base 

 with the water-vascular system. 



development at the same time — an impossible thing to 

 describe or figure — and this is where our difficulty comes 

 in. For while the parts mentioned would be taking shape, 

 others would be evolving in their company, moreover 

 influenced by them and influencing them. While the head 

 and narrow gullet were forming, accompanying alimentary, 

 respiratory, and circulatory novelties would be developing. 

 As a mass of solid tissues, the developing head would not 

 rhythmically contract, but below it there would be taking 

 shape a sac -like body whose walls would contract in a wave- 

 like manner — a gift from ancestral medusoid bells. These 



