VI EVOLUTION IN BIOLOGY 203 
Nevertheless, though the doctrine of epigenesis, 
as understood by Harvey, has definitively triumphed 
over the doctrine of evolution, as understood 
' by his opponents of the eighteenth century, 
it is not impossible that, when the analysis of the 
process of development is carried still further, and 
the origin of the molecular components of the 
_ physically gross, though sensibly minute, bodies 
_ which we term germs is traced, the theory of de- 
velopment will approach more nearly to meta- 
morphosis than to epigenesis. Harvey thought 
__ that impregnation influenced the female organism 
as a contagion ; and that the blood, which he con- 
ceived to be the first rudiment of the germ, arose 
_ in the clear fluid of the “ colliquamentum ” of the 
ovum by a process of concrescence, as a sort of 
living precipitate. Wenow know, on the contrary, 
that the female germ or ovum, in all the higher 
_ animals and plants, is a body which possesses the 
\ 
structure of a nucleated cell; that impregnation 
_ consists in the fusion of the substance! of another 
more or less modified nucleated cell, the male germ, 
with the ovum; and that the structural com- 
“ponents of the body of the embryo are all derived, 
by a process of division, from the coalesced male 
and female germs. Hence it is conceivable, and 
indeed probable, that every part of the adult con- 
tains molecules, derived both from the male and 
' [At any rate of the nuclei of the two germ-cells. 1893]. 
