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2 



HTDROZOA. 



ovum in its turn, then, that ovum, if fertilised 

 forms the basis of a new individual ; and so on 

 for every additional ovum concerned in a genera- 

 tive act. So that each performance of the repro- 

 ductive process is, as it were, the natural boundary 

 between two successive individuals, or, in other 

 words, between two distinct cycles of development. 

 Thus, while the individual perishes, the species, 

 by reproduction, is constantly renewed. Much 

 also, might be said on the analogy which exists 

 between the different individuals of the 

 species, on the one hand, and the constituent parts 

 of each individual, on the other. 



Again, fission and gemmation are not, as many 

 writers incorrectly state, modifications of the re- 

 productive process, but rather, acts of development. 

 For, as already shown, every ovum is at first a 

 bud, which at length, by fission, becomes separated 

 from the body of the parent. All this takes place 

 quite independently of its fecundation. So that 

 an unfertilised ovum is no more entitled to be 

 considered an individual , than a wart or any other 

 excrescence. 



The antagonism between development and re- 

 production, or even between development in 

 general and those particular stages of the vital 

 process by which reproduction is preceded, is 

 sometimes shown by the fact that certain external 

 conditions which seem to favour the one exert an 

 opposite influence on the other. Thus, on the 

 approach of cold weather, the Hydra is prone to 

 develop organs of true reproduction, while, if 

 kept in a warm room, it still, as in summer time, 

 continues the formation of ordinary buds. 



It is, therefore, the object of the reproductive 



