230 THE EVOLUTION OF SEX. 



asexual hydroid or hydra-tuba, and the active sexual medusoid 

 or jelly-fish, is very marked. So too, on a higher plane, the 

 vegetative spore-producing fern-plant stands opposed to the less 

 nutritive sexual prothallus. The alternation is but a rhythm of 

 large amplitude between anabolic and katabolic preponderance. 



What is so marked in the alternation is only a special- 

 isation of the reproductive or sexual parts of the organism as 

 against the growing or asexual ones, — a specialisation which 

 becomes exaggerated into separate existences, each dominated 

 by its own physiological bias. 



In the fern or flowering plant the vegetative or asexual 

 existence has preponderated, and this is entirely consistent 

 with the characteristic passivity of plants. This is emphatically 

 their line of development; but, be it observed, that though 

 in the flowering plants the nutritive generation has dwarfed, 

 and included the sexual, which seem indeed to be mere 

 organs, — the pollen-grain and embryo sac, — yet it is through 

 and for these that we have all the glory of the flower (see fig. 

 p. 211). In animals, with their emphatically active line of de- 

 velopment, the reproductive generation is the higher ; and in 

 the higher forms the separate asexual existence is wholly lost. 



