50 LIFE OF ELIE METCHNIKOFF 



worked with the greatest energy, going together on 

 zoological excursions, exchanging their ideas, dis- 

 cussing their aspirations ; a similarity of tastes lent 

 great attraction to their friendship. 



At Giessen, EUe had read Fritz Miiller's For 

 Darwin, a book which had a decisive influence on the 

 future direction of his researches. Fritz MiiUer, in his 

 embryological works on certain crustaceans, had been 

 the first to confirm in a concrete manner Darwin's 

 evolutionist theories ; he had thus demonstrated that 

 it was chiefly in embryology that precious indications 

 were to be found concerning the genealogy of organ- 

 isms.^ Under the influence of this work, Elie, who 

 until now had limited himself to introductory re- 

 searches, resolved to concentrate aU his efiorts on the 

 comparative embryology of animals. He started to 

 work in that direction, and his researches confirmed 

 him more and more in the opinion that the key of 

 animal evolution and genealogy was to be sought for 

 in the most primitive stages, in those simple phases 

 of development where no secondary element has yet 

 been introduced from external conditions. In those 

 primordial stages, essential characters, common to 

 aU, reveal the analogy and connections between 

 animals from different groups. 



Every animal begins by being unicellular, for the 

 egg-cell, the reproducing ceU, common to aU, corre- 

 sponds to a unicellular being. It is only after fecunda- 

 tion, when it has become an ovum, that this first 

 ceU evolves by dividing itself into consecutive 

 segments, each of which is a new ceU. This pheno- 

 menon is analogous with the multiplication of uni- 



1 In later years MetohnikofE often dwelt on the fact that Fritz MiiUer 

 was not fully appreciated and that it was he who had most efficaciously 

 contributed to the confirmation of Darwinian theories. 



