126 THE EVOLUTION OF CONTINUITY 



bell, so that steady locomotion and respiration may take 

 place, the latter in the form of a regular drive of fresh contents 

 through the canal system. Thus we might regard the 

 circular ganglionated cord as the primitive central nervous 

 system, for it controls circulation, respiration, and locomotion, 

 and probably commands the action of the diffuse nervous 

 layer which controls the actual tissue cells. 



Where the Individual is, like the compound Coral, con- 

 tinuously megazooidal, or a colony of units on the plan of 



a B 



Fig. 45. — A, cross-section of sea-anemone's tissue layers (magni- 

 fied), showing ganglion cells (g) and nerve-fibres (n) lying 

 between the ectoderm (ec) and the mesoderm (in, I) ; en, the 

 endoderm. b, greatly magnified view of ganglion cells and 

 nerve-fibres. (Nicholson.) 



the sea-anemone, each corallite controls its own functions 

 as does this organism. Naturally, as environmental influ- 

 ences, the corallites may affect each other. 



Passing aside to the Radiate Individual, we find a " central 

 nervous system " similar to, but more advanced than that of 

 the medusoid, there being a circular ganglionated nerve-cord 

 which we take to be of medusoid derivation. In addition, 

 however, there are radial nerve-cords which pass down 



