PRESENT TENDENCIES OF MORPHOLOGY 265 



vidual development of the forms which are permanently realized 

 in the actual zoological series. But this idea could not be fully 

 understood and bear all its fruits until it was completed and solidly 

 demonstrated by Fritz Miiller in his admirable little book Fur 

 Darwin, 



From that time the triple parallelism existing between the zoo- 

 logical series, the ontogenetic series and the paleontological series, 

 appeared as a necessary consequence of the phylogenetic kinship 

 of animals, and as the evident interpretation of their genealogical 

 relations. Furthermore, as should happen in the application of all 

 serious theories, the apparent exceptions due to abbreviations or 

 to falsifications of ontogenetic evolution may be foreseen and ex- 

 plained partly by the principles of the Darwinian doctrine: natural 

 selection and the struggle for existence. 



It is then with good reason that the principle of Serres and of 

 Fritz Miiller has been called by Haeckel the fundamental bio- 

 genetic law, if we give to this word law the meaning that we ordin- 

 arily give it in experimental sciences, that of a general formula 

 susceptible of sufficient verification and permitting us indefinitely 

 to predict new facts. Rich in the works of Daubenton, of Haller, 

 of Camper, of Pallas, of Vicq d'Azyr, comparative anatomy seemed 

 to have received from the genius of Cuvier forever indestructible 

 foundations. 



It could not escape, however, from the renovating action of evo- 

 lutionary ideas. The problems that it always had in view, the ques- 

 tions that it apparently had answered, soon reappeared in improved 

 forms; Huxley, Gegenbaur, Leuckart were not slow to show us in 

 what direction definite solution was to be sought. 



The pretended law of the correlation of forms (Cuvier), the prin- 

 ciple of connections (Et. Geoffrey Saint-Hilaire), that of the balanc- 

 ing of organs, the idea of the degeneration of types (de Blainville), 

 the notion of rudimentary organs, etc., instead of being simple 

 empirical formulas, became the synthetic expression of real and 

 necessary relations between organisms related by consanguinity, and 

 if they had not already been firmly established inductively, these 

 conceptions could have been deduced as the necessary corollaries 

 of the genealogical kinship of living beings. 



If we turn to the memoirs of the period and to the famous dis- 

 cussion between Cuvier and Et. Geoffroy Saint-Hilaire concerning 

 the unity of organic structure, a discussion in which Goethe followed 

 the Peripatetics with so much passion that he concentrated the 

 strength of his mind upon it to the neglect of the political revolution 

 which occupied every one in 1830, we recognize with astonishment 

 that neither the one nor the other of the illustrious adversaries 

 appreciated the much greater significance the debate would have 



