MEGAZOOIDAL INDIVIDUALS 



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but it is commonly taken for granted that as it is borne 

 by a zooidal colony it is a glorified zooid of sorts in which 

 the ordinary mouth-tentacles have become radial canals. 

 There seems to be no grounds for this view, but, on the 

 contrary, and consistently with the whole theory of the 

 evolution of living Continuity, there is good reason to believe 

 that the organism is megazooidal, and that the radial canals 

 represent the blind, tubular, central spades of ancestral 



Fig. 31. — i, vertical section (very diagrammatic) of a sea- 

 anemone, passing through two intermesenteric chambers. 

 m, the mouth ; </, oesophagus ; cs, coelenteric space ; ic, inter- 

 mesenteric chambers ; ec, ectoderm ; ere, endoderm ; J, 

 jelly tissue between these layers, and comparatively poorly 

 developed, n, vertical section of a diagrammatic medusi- 

 form gonophore, dividing a radial canal in its length, re, 

 radial canal, corresponding to ic in I. cc, circular canal cut 

 transversely ; it has no equivalent in I. t;, edge of velum. 

 The other letters have the same significance as in I. The 

 jelly tissue here is enormously developed except at cm, where 

 it is represented by tbe circular muscle at base of the velum. 

 Most important of all, we have the space, x, in ll — a feature 

 non-existent in I, where one layer each of ectoderm, jelly, 

 and endoderm serves for the oesophageal tube and the inner 

 wall of the intermesenteric chamber, ic. 



sporosacs which arose from a tubular stem. The radial 

 canals, lined as they are with endoderm, have, it is suggested, 

 a derivation parallel to that of the intermesenteric chambers 

 of the sea-anemone ; in fact, were the canals to be dilated 

 so that they were in lateral contact with each other and 

 with the central manubrium, the plan would be roughly 

 that of the sea-anemone. 



But the radial canals are comparatively narrow, and this 



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