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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    THE TREMATODA. & ] I have, however, satisfied myself that very far from all the individuals reach the organs mentioned above, viz., the liver and generative organs; for I have observed great numbers of them full-grown which could not be distinguished from those m the liver, occupying the ca- vity in the head and anterior part of the body which is filled with a slimy fluid, and in which the nervous ring of the pharynx is situated, in the cavity around the heart, and in several other situations, so that this Disfoma is not one of those species whose full development is re- stricted to one organ of the animal infested by them. We have thus again traced a free swimming Cercaria or Distoma-larva, until it is deposited as a true entozoon Distoma or fluke, deep in the organs of the snail; we shall now see that it has previously inhabited, also, the interior of a snail, although not of the same one. ‘The observations already referred to of Bojanus, Baer, and Siebold, have proved that all Cercarie occur in sacciform bodies in the interior of snails, and the sacs ın which these animals are situate have been described by Siebold, in Burdach’s ‘ Physiologie,’ 1.c. The figures 1,/ and lg represent sacs of this kind, containing numbers of developed and undeveloped Cercarie ; and if one of these sacs is opened, the whole series of forms through which the Cercari@ pass can be readily followed (figs. 2 a—v,) from the globular gemmules to the perfect forms, which as soon as they have quitted the sac, can no longer be distinguished from those swimming free in the water. It may be soon ascertained that the whole course of de- velopment entirely corresponds with that of the former species. The parts which are completed last are the frontal spiculum and the double tortuous organ, which passes down on each side of the body. By the first inquiries it was soon determined that «U Cercarie originate in the sacciform bodies, and that these always contain Cercarie, and grow and are de- 6