Chap. XKV1L OF PANGENESIS. 361 



successive bud-generations, yet they occasionally revert, even 

 after a long series of bud-generations, to their former character. 

 This tendency to reversion in buds is one of the most remarkable 

 of the several points of agreement between the offspring from 

 bud and seminal reproduction. 



There is, however, one difference between beings produced 

 sexually and asexually, which is very general. The former 

 usually pass in the course of their development from a lower to 

 a higher grade, as we see in the metamorphoses of insects and 

 in the concealed metamorphoses of the vertebrata ; but this 

 passage from a lower to a higher grade cannot be considered as 

 a necessary accompaniment of sexual reproduction, for hardly 

 anything of the kind occurs in the development of Aphis 

 amongst insects, or with certain crustaceans, cephalopods, or 

 with any of the higher vascular plants. Animals propagated 

 asexually by buds or fission are on the other hand never known 

 to undergo a retrogressive metamorphosis ; that is, they do not 

 first sink to a lower before passing on to their higher and final 

 stage of development. But during the act of asexual produc- 

 tion or subsequently to it, they often advance in organisation, 

 as we see in the many cases of " alternate generation." In thus 

 speaking of alternate generation, I follow those naturalists who 

 look at the process as essentially one of internal budding or of 

 fissiparous generation. Some of the lower plants, however, such 

 as mosses and certain algae, according to Dr. L. Eadlkofer, 7 when 

 propagated asexually, do undergo a retrogressive metamorphosis. 

 We can to a certain extent understand, as far as the final cause 

 is concerned, why beings propagated by buds should so rarely 

 retrogress during development; for with each organism the 

 structure acquired at each stage of development must be adapted 

 to its peculiar habits. Now, with beings produced by gemmation, 

 —and this, differently from sexual reproduction, may occur at 

 any period of growth,— if there were places for the support of 

 many individuals at some one stage of development, the simplest 

 plan would be that they should be multiplied by gemmation at 

 that stage, and not that they should first retrograde in their 

 development to an earlier or simpler structure, which might 

 not be fitted for the surrounding conditions. 



7 < Annals and Mag. of Nat. Hist.' 2nd series, vol. xx., 1857, pp. 153-455. 



