CHAPTER XI 



THE DISCONTINUOUSLY MEGAZOOIDAL 

 INDIVIDUAL. THE CONTINUOUSLY 

 MEGAZOOIDAL INDIVIDUAL 



The Monomegazooidal Individuals have not been milestones 

 on Evolution's main road as, apparently, certain Polymega- 

 zooidal Individuals have been. For it would appear that a 

 polymegazooidal Individual, or one composed of many mega- 

 zooids, was the primitive ccelenterate type from which 

 evolved the Vertebrata. The straight road of the evolution 

 of Continuity is therefore regarded by us as passing on 

 from the Continuously Zooidal to the Discontinuously 

 Megazooidal Individual. 



The DisooNTiNixotrsLY Megazooidal Individual. 



The component megazooids are here medusoid in struc- 

 tural plan, and enjoy an independent free-swimming existence. 

 In the illustrative example which has been chosen it is 

 true that there is a temporary exhibition of continuity, 

 but as the megazooids ultimately all become discontinuous 

 the above designation of the Individual may be taken as 

 correct. Our example is Aurelia, a member of one of the 

 main sub-divisions of the Hydrozoa which is called the 

 Lucernarida, this being a zoological classification which does 

 not take into account the question of Continuity's evolution. 



In Aurelia the Individual begins life as a ciliated oval 

 embryo, possessing a hollow interior. The embryo in time 

 attaches itself to some underwater object and gradually 

 takes the form shown in Fig. 34, 6 ; in fact, it becomes an 

 attached medusoid, possessing a central manubrium with 

 a mouth opening at the distal end, and an umbrella sup- 

 porting marginal tentacles and supplied with a complete 



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