THE EVOLUTION THEORY. 



291 



heredity, the different states assumed under our 

 own eyes in a very brief period by the embryo 

 are simply a condensed and abridged summing up 

 of the corresponding form-changes through which 

 the ancestors of the form underexamination have 

 passed in the course of ages. From a hen's-egg, 

 placed in a hatching apparatus, we see coming 

 forth after twenty-one days a young chick ; we 

 are no longer mute with wonder at the marvel- 

 ous changes which conduct us from the simple 

 ovula-cell to the gastrula, from the gastrula to 

 the vermiform and acephalous embryo, and from 

 the latter to the higher embryonic forms which 

 present the organization of a fish, an amphibian, 

 a reptile, and finally a bird. What is more, we 

 from all this infer the series of corresponding an- 

 cestral forms from the unicellular amoeba to the 

 gastraa, and so on through Vermes, Acrania, 

 Fishes, Amphibia, and Reptilia, to the Birds. 

 Thus does the series of embryonic forms in the 

 chicken present to us a sketch-list of its real 

 ancestors. 



The direct, original connection, then, which ex- 

 ists between the embryology of the individual and 

 the genealogical history of its ancestors, con- 

 stitutes our fundamental biogenetic law, and is 

 summed up in this brief expression : embryology 

 (or ontogeny) is a synopsis of genealogy (or phylo- 

 geny), the laws of heredity being the condition. 

 This palingenetic abridgment is momentarily dis- 

 turbed only when there appear, in consequence 

 of adaptation to the conditions of embryonic life, 

 cenogenetic modifications. 



The phylogenetic meaning of embryological 

 phenomena is the only explanation we can offer 

 of them as yet — an explanation that is confirmed 

 in the highest degree and completed by the re- 

 sults of comparative anatomy and paleontology. 

 The truth is, that this matter does not admit of 

 exact or even experimental demonstration. For 

 all these biological data, from the very nature of 

 things, have to do with historical and philosophi- 

 cal natural science. Their common aim is to dis- 

 cover historic facts which, in the lapse of many 

 thousands of years, took place on the surface of 

 our young planet, long before the coming of the 

 human race. Direct, exact demonstration of them 

 is a thing utterly beyond the limits of possibility. 



By a critical study of the historical archives, 

 and by a prudent though bold use of speculative 

 hypothesis, we may indirectly come at the truth. 

 Phylogeny turns these historic data to account, 

 and determines their significance after the same 

 manner as the other historical sciences. Just as 

 the historian, with the aid of chronicles, biog- 



raphies, and private letters, faithfully describes 

 for us events that occurred long ago; as the 

 archaeologist, from the study of sculptures, inscrip- 

 tions, utensils, learns the grade of civilization 

 reached by a people that long since disappeared ; 

 as the philologist, by comparing kindred lan- 

 guages, whether in their present state or in their 

 most ancient documents, shows that they have de- 

 veloped and that they have their source in a com- 

 mon mother-language — so the naturalist, by mak- 

 ing critical use of the phylogenetic archives of 

 comparative anatomy, ontogeny, and paleontology, 

 acquires an approximately correct knowledge of 

 the facts which, in the lapse of untold ages, have 

 brought about changes in the forms of organic 

 life upon the earth. 



The genealogical history of organisms or phy- 

 logeny cannot rest on foundations more exact, 

 more experimental, than its elder and more fa- 

 vored sister, geology. Nevertheless the scientific 

 value of the latter is now universally recognized. 

 Only an ignorant person can now smile incred- 

 ulously on being told that the mighty ranges of 

 the Alps, whose snow-capped crests glisten from 

 afar, consist simply of indurated sea-ooze. The 

 stratification of these mountains, and the fossils 

 imbedded in them, admit no other explanation, 

 though the thing is incapable of exact demon- 

 stration. All geologists to-day agree in admit- 

 ting a succession, a fixed classification of these 

 Alpine strata, though this classification presup- 

 poses a stratigraphic system that nowhere exists 

 unbroken. Do not our phylogenetic hypotheses 

 possess the same value as these generally-accepted 

 geological hypotheses ? The only difference be- 

 tween them is that this vast hypothetical ensem- 

 ble of geology is incomparably more perfect, more 

 simple, more easily comprehended, than that of 

 phylogeny, which is still young. 



The historical sciences of Nature, geology 

 and phylogeny, constitute a strong bond between 

 the exact natural sciences on the one hand, and 

 the purely historical, intellectual sciences on the 

 other. Thus does biology in general, but particu- 

 larly systematic zoology and botany, rise actually 

 to the grade of natural history — a title of honor 

 which they have long borne, but which they de- 

 serve only in our own time. If these sciences are 

 still oftentimes designated, and even in official 

 quarters, " descriptive " sciences, as distinguished 

 from the "explicative" sciences, that fact only 

 shows how erroneous an idea people have hith- 

 erto had of their true scope. Since the natural 

 system of organisms has come to be regarded as 

 the expression of their genealogy, systematics, 



