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. We now 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 l 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 



1 [At any rate of the nuclei of the two germ-cells. 1893], 



