OenerndutiSj MetamorjJio:iis, dc. '^) 



III other words, alternatiou of gencrutioiis was universally 

 tiie most primitive form of ontogeny, ami consequently it is 

 not of merely secondary origin through selection, hut, on the 

 contrary, it lias persisted only here and there. Thus, on the 

 basis of the theory of descent and the biogenetic law of re- 

 capitulation we arrive at this simple explanation: —alternafion 

 of generations is (nothing more than) (heonto/eiietic repetition 

 of the phijlogenetic progressive dcvilupneat from lower 

 organisms with asexual reproduction into higher species loith 

 dissociated sexual products. In this way, too, the different 

 varieties (beterogony &c.) are easily intelligible. 



When, in consequence of continued acceleration ot tbe 

 ontogeny, the first asexual generation produces, instead of 

 the previous numerous progenj, only a single offspring, and 

 when, moreover, this single descendant no longer severs itselt 

 from the mother, but proceeds from it more or less con- 

 tinuously, the ontogeny assumes the form of mrtamorphosis. 

 'J'he latter has therefore arisen from alternation of generations 

 by a process of constant abridgement ; and thus we can 

 shortly define metamorphosis as a curtailed alternation of 

 generations. 



In all cases, then, it is only through continuous aceeleration 

 of the ontogeny that direct development, as we find it to-day, 

 lias arisen from alternation of generations and metamorphosis. 

 Direct development is everywhere the secondary process, 

 which in constquence of its great rapidity is also well-nigh 

 incomprehensible, whereas it is much easier for us to picture 

 to ourselves phylogeny, which is a million times slower, and 

 also an earlier and less rapid ontogeny. 



In this way, therefore, alternci^ion of generations and 

 metamorphosis lose all that was previously inexplicable and 

 become easily intelligible to us by means of the theory of 

 descent, when we regard them simply as ontogenetic recapitu- 

 lations of the development of the species. They are no new 

 processes, which have only arisen at a later date, but, on the 

 contrary, the oldest forms of ontogeny, which, on a further 

 development of the organic world, should it chance to occur 

 later on, will tend towards direct development, but have not 

 originated from the latter. Their occurrence t j-day represents 

 only tiie last remnants of earlier and probably much more 

 widely diffused conditions, just as is the case as regards 

 modern parthenogenesis. 



A material advantage of this mode of interpretation, there- 

 fore, is that it is nowhere necessary for us to assume the 

 existence of a cwnogenesis, with retarded and altered develop- 

 ment. Ontogeny consequently makes no detours, but merely 



