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Show 360 PROVISIONAL IIYPOTIIESl tl C IIAP. X X \ ' [[ , quently, become developed into perfect beings, without the concourse of the male element. J. Muller and others admit that ovules and buds have the same essential nature. Certain bodies, which during their early development cannot be distinguished by any external character from true oYules, nevertheless must be classed as buds, for though form ed within the ovarium they are incapable of fertilisation. This is the case with the germballs of the Cecidomyide larvre, as described by Leuckart.5 Ovules and the male element, before they become united, have, like buds, an independent existence. 6 Both have the power of transmitting every single character possessed by tl1e parentform. vVe see this clearly when hybrids are paired inter se, for the characters of either grandparent often reappear, either perfectly or by segments, in the progeny. It is an error to suppose that the male transmits certain cl1aracters and the female other charact ers; though no doubt, from unknown causes, one sex sometimes has a stronger power of transmission than the other. It has been maintained by some authors that a bud differs essentially from a fertilised germ, by always reproducing the perfect character of the parent-stock; whilst fertiliscrl germs beeome developed into beings which differ, in a greater or less degree, from each other and from their parents. But there is no such broad distinction as this. In the eleventh chapter, numerous cases were given showing that buds occasionally grow into plants having new aud strongly markeu characters ; and varieties thus produced can be propagat ed for a length of time by buds, and occasionally by seed. Nevertheless, it must be admitted that beings produced sexually are much more liable to vary than those produced asexually ; and of this fact a partial explanation will hereafter be attempted. The variability in both cases is determined by the same general causes, and is governed by tho same laws. Hence new varieties arising from buds cannot be distinguished from those arising from seed. Although bud-varieties usually retain their character during s On the Asexual Reproduction of Cecydomyicle Lo.rv:B, translated in 'Annals and Mag. of Nat. I·Iist.,' Ma.rch 1866, pp. 167, 171. 6 See some excellent rem:-trks on this head by Qu:-ttrefages, in 'Annales des Sc. Nat.,' Zoolog., ·3rd series, 1850, p. 108. CllAP. XXVII. OF PANGE.c~ESIS. ~ 361 snccessive 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 sexua1ly 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 A phis 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 production or subsequently to it, they oft en 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 algre, according to Dr. L. Radlkofer,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 '<vould 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 aud Mag. of Nat. Hist.,' 2nd series, vol. xx., 1857, pp. 153-455. |