214 BIOLOGICAL LECTURES. 



expansions of parts predelineated in a miniature organism. 

 With Harvey we may say, that in the egg, " no part of the 

 future offspring exists de facto, but all parts inhere in poten- 

 tia " (Ex. XXVI). But we do not mean it quite as he meant 

 it. We mean it with a reservation not anticipated in his 

 theory a reservation which is at once the foundation, and 

 the essence, of the modern doctrine of homogenesis, as contra- 

 distinguished from agenesis, or abiogenesis, and xenogenesis. 



Continuity of organization is indeed a species of preforma- 

 tion, but it is a preformation which no one will now deny, who 

 accepts the fact reached over so many battle-grounds, that 

 germs are not produced epigenetically, but by division of preex- 

 isting germs. "It is certain," says Huxley, "that the germ is 

 not merely a body in which life is dormant or potential, but 

 that it is itself simply a detached portion of the substance of a 

 preexisting living body" ("Evolution in Biology," Darwiniana 

 Essays, II, p. 198). To this extent we are all preformation- 

 ists, nolens volens. 



We are no longer in the position of the philosophers of last 

 century, who were still totally blind to the central fact of 

 modern biology the law of genetic continuity, first neatly 

 embodied in Virchow's formula : omnis cellula e cellula, but 

 since extended to every order of vital unit within the cell, and 

 raised to the full dignity of a general law by the final abandon- 

 ment of the hypothesis of spontaneous generation. 



The law of genetic continuity is to the biologist what the 

 law of conservation of energy is to the physicist. It abolishes 

 the miracle of original creation. It sets the individual up, not 

 as a separately made instrument, but as a vital link in a con- 

 tinuous series of developments. It gives heredity a rational 

 basis, reduces it to a formula that accords with the physical 

 law. It enables us to see what before could not be divined, 

 that preformation involves no miraculous intervention of a 

 supernatural agency. It enables us to view germs, not as de 

 novo creations, but as complex products, embodiments of work 

 previously done. It puts in a clear light the fact that organi- 

 zation can be, and actually is, directly transmitted. It shows 

 us how the whole organic world hangs on the power of growth 



