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
Catalogue details

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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    inner surface of the bell, directly opened. Midway between these four canals, under favorable circumstances and with a good hght might be observed some fine lines, which I looked upon as smaller canals of the same kind. During the first few days in which the animals were under my observation, I perceived no other internal organs; but at a later period, I observed at the bottom of the cavity of the body, a four-sided projection (figs. 36 and 38,) in which there was a hollow, usually square. Frequently, when the bell and the annular membrane around its orifice were extended, I have seen this quad- rangular organ which is toothed at the extremity, become elongated and project as far as the orifice, bemg placed in the middle of the cavity like the clapper of a bell. At other times, when the body has been much depressed, so as not to be more than a quarter of its usual height, and has presented at its circumference, as it were, four lobes, this organ has projected more than half its length from the mouth of the bell (fig. 37;) on which account, I could no longer in any way doubt, that it was really an oral opening and cesophagus, such as we find in the Meduse, as for mstance in the maternal animal, the Medusa aurita. But besides this point of resemblance we actually find also a vascular system, consisting of annular canals, connected by radiating vessels, and resembling that system of organs in the full-grown animal, together with a number of ten- tacula, which are produced gradually and in a definite order, like the tentacula of the self-developing Meduse, in a word we recognize im this apparently polypoid animal, an actual Medusa, but which is fixed. These polypiform Meduse thus enjoy a mode of de- velopment peculiar to themselves before the period at which Medusa-larve are formed in their abdomen (if such a term may be here applied,) and there is no observation to show that they undergo any further development after the formation and detachment of the /arve ; on the con- trary, it has been observed that when the larvae approach the complete term of their growth, the trunk or stem is found without such polypoid animal upon it.