74 THE EVOLUTION OF CONTINUITY 



sexual ; the number depending on the " stage " the zooid 

 represents in the cycle. 



II. That the zooid's sexual organs will finally appear in 

 what we have called gemmation-areas. It is probable, how- 

 ever, that gemmation is carried on with special frequency 

 at two such areas. 



The interesting fact, that if a Hydra zooid be cut in 

 pieces each piece grows to form a new and perfect zooid, 

 illustrates well the law that whereas Continuity produces 

 Arrest, Discontinuity produces Release from Arrest. The 

 matter is one of breach of Continuity, and the artificial 



Sol 





v> 





Fig. 17. — Possible zooidal progressive diminution A, an 

 initial or intermediate zooid originates B ; B originates c, and 

 so on, till the line ends with the sexual zooid at F. The suc- 

 cessive primary side-lines arising from the main line are repre- 

 sented as progressively diminishing by one zooid. 



release from cell-arrest. Continuity being severed, the cells 

 exposed are released to multiply till the parts lacking from 

 the original zooidal plan are restored. 



It is also to be noted that " alternation of generations " 

 is exhibited in the Hydra cycle. There is cellular alternation 

 in that asexual cells appear, and remain, as stages on the 

 road to the final exhibition of sexual cells ; and there is 

 zooidal alternation in that temporarily asexual zooids become 

 sexual in the end, and in this sense alternate with sexual 

 zooids. It may be objected that this is not alternation of 

 generations in the true sense, as for example in the case 

 of the Hydrozoal colony, but in reality the cases are the same, 

 the striking picture presented by the colony being the result 

 of zooidal Continuity and Arrest. As, however, we shall 



