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MICROSCOPICAL INVESTIGATION. 367
to these dreams by confirming the -view of the high import­
ance of the ovum for the development of the human
embryo; and yet he committed the error of considering the
spermatozoa as an unessential accidental constituent of the
semen, and of declaring them to be without effect in
generation. This view was also countenanced by BUFFON,
HALLER, and others, and obtained almost universal accept­
ance. SPALLANZANI was the first once more to submit to a
closer investigation the problem of the real cause of im­
pregnation, and with this object undertook a series of
experiments in artificial impregnation with the spermatic
fluid of the male.* HALLER afforded valuable information
upon the development of the embryo, especially upon the
formation of the vascular system. The fcetal circulation
was thoroughly explained by DuVERNEY.
Most philosophers gave credence to the old theological
theory of development, according to which the germs of
organic beings are preformed from the time of the creation
of the first, and lie embedded in one another like a series of
boxes, each enclosing a smaller one. This view of things
was replaced by the doctrine of Epigenesis, in which
CASPAR FRIEDRICH WOLFF, as the result of a great number
of careful observations, delivered his opinion that organs
have not existed in their mature shape from the beginning
of things, but that the particular parts of the body assume
gradually their fully-developed form as the result of a series
of differentiations.! With great penetration he referred to
the analogous development of plants and animals, and in
this connection even pointed to the doctrine of metamor­
phosis in the vegetable kingdom further developed by
GOETHE. He also made the observation that the nervous
system, the alimentary canal, and the vasculo-muscular
* SPALLANZANI : Versuche uber die Erzeugung der Thiere und Pflanzen,
Deutsche Ubers., Leipzig 1786.
t C.F.WOLFF: Theoria generationis, Halle 1759.—C. F. WOLFF: Uber die
Bildung des Darmkanals im bebruteten Huhnchen, Berlin 1812 S sv 12K
148.
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