ALTERNATION OF GENERATIONS 243 



peculiar structure of the latter. Frequently the repro- 

 ductive entity is a megazooid and not a zooid (Fig. 83). 



becomes 



Fio. 82. — Alternation of cycle-stages in the Discontinuously 

 Zooidal Individual. 



VI. The Discontinuously Megazooidal Individual. — Owing 

 to discontinuity, the sexless megazooids all ultimately 



Fig. 83. — Alternation of cycle-stages in the Continuously 

 Zooidal Individual. In a, the vegetative zooid, v, contrasts 

 with the sexual zooid, or sporosac, s. In b, the contrast is 

 with a sexual megazooid, or gonophore, g. 



become sexual (as in I and IV). The alternation is cellular 

 and megazooidal ; the example being Aurelia (page 103). 



