MEGAZOOIDAL INDIVIDUALS 105 



sented solely by free-swimming gonophores. It is thus of 

 a higher type than the Continuously Zooidal Hydrozoa 

 which, though producing medusiform gonophores, develop 

 as a whole zooidally. 



The Continuously Megazooidal Individual. 



This is simply a colony of megazooids produced by some 

 form of continuous gemmation — that is, all remain attached 

 to each other — and it is to the Compound Corals that we 

 turn for examples (Fig. 36). 



The above illustration shows a colony of megazooids 

 produced by continuous gemmation ; a colony of compressed 

 " zooid-multiples." And the plan of each megazooid is 

 similar to that of the Sea-anemone. But the size of the Coral 

 megazooid is generally very much smaller, and the organism 



Fig. 36. — A small part of a compound coral, Astrcea pallida. 

 Some corallites have their tentacles extruded. (Diagrammatic, 

 after Nicholson, after Dana.) 



is only part of an Individual ; while in addition it possesses 

 a calcareous skeleton secreted by the soft parts, or formed 

 by the calcification of the branching coenosarc. Fig. 37, 

 although the cross-section of a " simple " Coral, represents 

 equally well the plan of the corallite of the Compound 

 Coral. 



Thus, whereas in the Continuously Zooidal Individual 

 we have zooidal serial Continuity, in the Continuously 

 Megazooidal Individual we have megazooidal serial Con- 

 tinuity, a discontinuous Individual type intervening. In 

 Fig. 36 the serial Continuity is not very obvious owing to 

 the fact that the corallites successively produced grow 

 closely together. Each is nevertheless a connecting link 

 in some megazooidal branching series, and there is no true 

 lateral Continuity, the corallite living practically an inde- 

 pendent existence. 



