Metamorphoses of man and the lower animals / by A. de Quatrefages ; translated by Henry Lawson.

Date:
1864
Catalogue details

Licence: Public Domain Mark

Credit: Metamorphoses of man and the lower animals / by A. de Quatrefages ; translated by Henry Lawson. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    yiscera of fresli-water mollusks there were developed — liow_, it was unknovm—beings called SporocystSj species of living envelopes^ provided witli a v/ell- marked digestive tube^ but always devoid of repro- ductive organs. Tliese sporocysts gave rise simul- taneously to new bodies like tkemselves, and to germs^ wbicli became developed into Gercarice, crea- tures in the form of tadpoles^ able to inhabit water, but of quite as neuter a ckaracter as tke others. These Cercariss were the necessary ]jarasites of the vSporocysts. After undergoing their development in the interior of the latter, the Cercarigs burst their walls and became encysted, somewhat like the di- pterous insects we spoke of in a preceding chapter, and terminated their short lives in the prison in which they were enclosed. We see that, according to this method of explaining observed facts, a sexless animal, of unknown origin, produces simultaneously, by gemmation, creatures like itself, and others of an entirely different character, which could never be directly produced. It would be idle to touch on the vague and evidently incom- plete nature of such ideas. Steenstrup, by his theory of alternate generation, threw a light upon these dark clouds, which seemed almost to lower in proportion as men laboured to dispel them. Supported by his own and his prede- cessors^ researches, he boldly classed the Bistomidm (Helminthes of the trematode group) side by side with the Corynid£e and Medusidae, in regard to their mode of reproduction. It was shov^n by the Danish savant, that the peculiar bodies then termed Sporocysts were the true nurses of the Trematodes, and that the