On tape and cystic worms : with an introduction on the origin of intestinal worms / by Carl Theodor von Siebold ; translated by T.H. Huxley.

  • Siebold, C. Th. E. von (Carl Th. Ernst), 1804-1885.
Date:
1857
Catalogue details

Licence: Public Domain Mark

Credit: On tape and cystic worms : with an introduction on the origin of intestinal worms / by Carl Theodor von Siebold ; translated by T.H. Huxley. Source: Wellcome Collection.

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

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    are, and remain, dissimilar to their parent, but bring forth a new generation, whose members either themselves, or in their descend- ants, return to the original form of the parent animal/' Any one who has not familiarized himself with the fun- damental idea of this doctrine of the alternation of generations, may easily imagine it to be nothing but a modification of the long well-known metamorphosis, exemplified by the tadpoles of frogs and toads, or by the larvse and chrysalises of most insects. This is, however, by no means the case. Those reptiles and insects that are subject to metamorphosis, no doubt bring forth young that diff'er from the parent, but there are two respects in which the act of simple metamorphosis widely difi'ers from the highly complex alternation of generations. Although Steenstrup has already particularly noticed these two grounds of difierence in his definition of the alternation of generations, I deem it not altogether superfluous on my part once more to draw especial attention to these important diver- gences, if only for the benefit of those who are unfamiliar with the phenomena. The first point of difierence between the alternation of generations, and metamorphosis, is, that the young of those animals whose mode of development comes under the former head, are not only unlike their parent at first, but remain so: the second distinction rests on the important fact that this yoimg generation, so dissimilar to the parent animal, brings forth new creatures, which either themselves, or in their descend- ants, revert to the original form of the first parent. Whereas, on the other hand, in simple metamorphosis, the dissimilar young pass by gradual changes into the likeness of the parent animal, and until this metamorphosis is complete, are incapable of generation. Steenstrup has given the name of nurse to those young, which, whilst departing from the parent type, remain, and propagate under their own form. It thus happens that in the alternation of generations (to use the words of Steenstrup), the parent animal produces nurses, whose descendants only, take her form. A most important circumstance which characterises these nurses or Agamozooids-^ ' I have rendered the word keim-korper by sporula, meaning thereby a free germ which is capable of development without fecundation, just as is the spore of a cryptogamous plant. When the sporula; are developed in a special organ I term this organ (the keimstock of Von Siebold) the sporularium. Any independent form from which sporulse or their equivalents alone are developed (the ammen or nurses of Von Siebold, Steenstrup, &c.) I terra agamozooids, See concluding note.—[Ed.]