ORGANIC DIFFERENTIATION 91 



not positively unscientific. Or sometimes in place of ex- 

 planations they have accepted certain a priori conceptions, 

 stated in the form of general laws borrowed from some 

 philosophical system or relegated to the sphere of Nature's 

 unfathomable mysteries. It is, indeed, owing to the difficulties 

 which heredity puts in the way of all explanations, that the 

 doctrine of special creation has arisen and persisted, contrary 

 to all reason. 



However, the function of heredity is not limited to the mere 

 conservation of characters, apart from the causes that have pro- 

 duced them. In the very act of conserving it must accumulate 

 them. This it is that Etienne Geoffroy Saint-Hilaire so 

 clearly perceived when he asserted that the embryos of the higher 

 animals reproduce the permanent forms of lower animals, i.e. 

 that they manifest, one after another, the characters acquired 

 by their various ancestors, which they must have inherited — 

 if, with Geoffroy Saint-Hilaire, we accept the theory of 

 evolution. The same truth is expressed with less precision 

 by the somewhat mystical formula of Antoine Serre, a disciple 

 of Geoffroy Saint-Hilaire : " Transcendental anatomy is only 

 a transitory comparative anatomy, just as comparative 

 anatomy is only a transcendental permanent anatomy." What 

 he called transcendental anatomy we now call embryogeny. 

 As we can study comparative anatomy only by considering the 

 series of forms, beginning with the simplest, that is to say the 

 oldest, and working up to the most complex, which are the 

 most recent, we come face to face with the formula of Haeckel, 

 which differs from the preceding ones only in its adaptation to 

 modern ideas : " The embryogeny of living organisms is 

 merely an abbreviated recapitulation of their genealogy." 



If we were to take this formula literally it would merely be 

 necessary to take the final expression of each organic series and 

 study it from the initial egg-stage to its full term of life, in order 

 to obtain an exact recapitulation of the entire past history of 

 the organisms now living on earth. True, we should still have 

 to reconstruct subsidiary lines that have now become extinct, 

 but we should be able to do this by means of the comparative 

 study of fossils as they succeeded one another. An accurate 

 knowledge of the laws determining the evolution of the series 

 actually represented to-day would permit us to fill the gaps with 

 extinct series, of which only a few fragments have been found. 



