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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    manner on a common polypidom and form a whole, or colony which, as regards the welfare of the species, stands in the same relation to it, that the hive of bees with its colony of three differently-formed broods of young, does to the bee species. It naturally follows that mention should here be made of the mode of propagation of the Salpe (Chap. IID), (although mdeed the observation of the worthy Chamisso has been otherwise interpreted, but m a way of which science has not availed herself, how- ever plausible the interpretation may have appeared to the superficial reader ;) and thus we have an alternation of generations, exhibited to us in the molluscous class, and it is certainly not confined to the Sa/pe only, but extends to all the compound Ascidians (Ascidie composite). In the class Hntozoa my researches have sufficed to prove not only the existence of such an “ alternation of Gene- rations,’ but to show besides, that traces of a similar mode of development are visible in almost a// the divi- sions of that class. According to recent observations it is, however, exhibited most clearly in the Zrematoda (Chap. IV), in which I prove that the Cercarie are the larve ot Distomata, and that they become true pupe ; that the animals in which the Cercari@ originate and grow up are peculiar Zrematode individuals, descended in the second or third generations from Distomata, and consequently not produced directly from their ova, but which, however anomalous they may at first sight appear, constitute a precedent generation having for its object the perfecting of the subsequent one. To similar observations belong also the description given long ago by Ehrenberg of the cyclical development of the Vorticelle, and the already long-known though misunderstood mode of propagation which obtains in the Aphides. The existence of an alternation of generations having in this way been established, not generally only, but even as it seems in all the lower classes, beyond doubt, it is