GENESIS. 213 



presented by these groups, arising from the fact that the 

 successive generations of sexless individuals produced 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-polypedom and 

 under going further development. Where, as in all 



the foregoing kinds of agamogenesis, the new individuals 

 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 entozoa of the genus Distoma, exhibit it. From the 

 egg of a Distoma, there results a rudely-formed creature 

 known to naturalists as the " King's-yellow worm." Gradu- 

 ally as this increases in size, the greater part of its inner 

 substance is transformed into young animals called Cercarice 

 (which are the larvse of Dlstomata) ; until at length, it 

 becomes little more than a living sac, full of living offspring. 

 In the Distoma pacifica, the brood of young animals thus 

 arising by internal gemmation, are not Cercarice, but are of 

 the same form as their parent : themselves becoming the 

 producers of Cercarice after the same manner, at a subsequent 

 period. So that sometimes the succession of forms is repre- 

 sented by the series A, B, A, B, &c. ; and sometimes by the 

 series A, B, B, A, B, B, &c. Both cases, however, exemplify 

 internal metagenesis, in contrast with the several kinds of 

 external metagenesis described above. That agamo- 



genesis which is carried on in a reproductive organ — either 

 a true ovarium or the homologue of one — has been called, by 

 Prof. Owen, parthenogenesis. In his work published under 

 this title, he embraced those cases in which the buds arising 

 in the pseud- ovarium, are not ova in the full sense of the 



