GENESIS. 273 



kingdom. Individuals developed from fertilized ova, instead 

 of themselves producing fertilized ova, produce, by gemma- 

 tion, strings of individuals from which fertilized ova again 

 originate. In multiaxial plants, we have a succession 



of generations represented by the series A, B, B, B, &c., A, B, 

 B, B, &c. Supposing A to be a flowering axis or sexual indi- 

 vidual, then, from any fertilized germ it casts off, there grows 

 up a sexless individual, B; from this there bud-out other 

 sexless individuals, B, and so on for generations more or less 

 numerous, until at length, from some of these sexless indi- 

 viduals, there bud-out seed-bearing individuals of the original 

 form A. Branched herbs, shrubs, and trees, exhibit this 

 form of heterogenesis : the successive generations of sexless 

 individuals thus produced being, in most cases, continuously 

 developed, or aggregated into a compound individual, but 

 being in some cases discontinuously developed. Among 

 animals a kind of heterogenesis represented by the same suc- 

 cession of letters, occurs in such compound polypes as the 

 Sertularia, and in those of the Hydrozoa which assume alter- 

 nately the polypoid form and the form of the Medusa. The 

 chief differences presented by these groups arise from the 

 fact that the successive generations of sexless individuals pro- 

 duced by budding, are in some cases continuously developed, 

 and in others discontinuously developed; and from the fact 

 that, in some cases, the sexual individuals give off their 

 fertilized germs while still growing on the parent-polypedom, 

 but in other cases not until after leaving the parent-poly- 

 pedom and undergoing further development. Where, 

 as in all the foregoing kinds of agamogenesis, the new indi- 

 viduals bud out, not from any specialized reproductive organs 

 but from unspecialized parts of the parent, the process has 

 been named, by Prof. Owen, metagenesis. In most instances 

 the individuals thus produced grow from the outsides of the 

 parents — ^the metagenesis is external. But there is also a 

 kind of metagenesis which we may distinguish as internal. 

 Certain cntozoa of the genus Distoma exhibit it. From the 



