REPORT 
ON THE 
CONTRIBUTIONS TO HELMINTHOLOGY, 
DURING THE YEAR 1842. 
BY 
PEOFESSOE C. TH. V. SIEBOLD OF EELANGEN. 
An Essay has been published by Steenstrup, “ Uber den Generations- 
wechsel oder die fortpflanzung und Entwickelung durch abwechselnde 
Generationen, eine eigenthiimliche Form der Brutpflege in den niederen 
ThierHassen, Copenhagen, 1842,” which will create an epoch in Hel- 
minthology, and be read by every Naturalist with the greatest interest. 
He has arranged, and attempted to point out, a series of remarkable 
phenomena, which have been discovered in the propagation of certain 
lower animals, but which could not hitherto be explained, and have 
therefore stood quite isolated ; that one and the same original idea is 
found expressed in them, which he designates by the name of {Genera- 
tionswechsel) transmutable generation. This original idea of nature is, 
that an animal bears a brood, which is neither like the mother-animal 
nor becomes so ; but this unlike-one itself brings forth a brood, which, 
in form and all other relations, returns to the mother-animal ; so that it 
again finds its like, not in its own brood, but in its successor of the 
second or third link, &c. In the orbicular Medusce and bulbous Polypi, 
Steenstrup has satisfactorily followed out this generation through its 
different links. Among the Helminthes, the Trematoda are particu- 
larly subject to such a change, and traces of it are found in various 
other orders of these animals. The reporter must completely assent 
to the intelligent view which Steenstrup takes of the remarkable 
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