On the alternation of generations; or, the propagation and development of animals through alternate generations: a peculiar form of fostering the young in the lower classes of animals ... / By Joh. Japetus Sm. Steenstrup ... Translated from the German version of C.H. Lorenzen, by George Busk.

  • Steenstrup, J. Japetus Sm. (Johannes Japetus Sm.), 1813-1897.
Date:
1845
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Licence: Public Domain Mark

Credit: On the alternation of generations; or, the propagation and development of animals through alternate generations: a peculiar form of fostering the young in the lower classes of animals ... / By Joh. Japetus Sm. Steenstrup ... Translated from the German version of C.H. Lorenzen, by George Busk. Source: Wellcome Collection.

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    species and genera are seen to be stages in the develop- ment of one and the same animal, &c. 4// these must be considered as secondary results,—as facts which are only adduced, so far as they serve to illustrate the fact of the “ alternation of generations.” In order to prevent my being further misunderstood, as I have repeatedly been in my oral exposition of this subject, and m the lately published Danish version of the work, I must remark that the phenomena, upon which my view of the alternation of generations rests, are, as every naturalist knows, new only in part, but that they have in this work received another, and, in my opinion, a natural explanation. They have generally been looked upon as instances of metamorphoses or transformation, the essential objection bemg overlooked, that a metamor- phosis can only imply changes which occur in the same individual; but when from it other mdividuals originate, something more than a metamorphosis is concerned. ‘Thus, it is quite erroneous to term a Scyphistoma the larval condition of Medusa aurita, since a Scyphistoma never becomes a medusa, but is the guası mother of some scores of them. Sars and Lovén have taken a more correct view of the relation m which these creatures stand with regard to each other, seeing in the development of the Meduse and Campanularie a series of generations under- going metamorphosis. It is of the more essential importance that the distinc- tion between an alternation of generation and a meta- morphosis should be understood, because a metamor- phosis may readily occur in one or other of the alternating generations themselves, as we see, for example, in the Distomata and Aphides. 'There is no transition from a metamorphosis to an alternation of generations, and a metamorphosis once commenced, cannot be continued beyond the generation, nor from the living or dead indi- vidual to another individual. I am not aware that any one has published concerning the alternation of genera-