44 GENESIS OF MAN. 



through which its race has passed during the long ages of its slow 

 development, and that the latter process is the strict physical and 

 mechanical cause of the former, — this deepest of all biological laws 

 Haeckel no longer treats as a theorem requiring demonstration, but 

 employs it as a postulate by the aid of which all the most trouble- 

 some gaps left in the anthropogenetic series by the evidences of 

 comparative anatomy, paleontology, and geographical distribution 

 (clwrology), are satisfactorily closed. Such gaps have existed along 

 the entire line, rendering it difficult and in many cases impossible 

 to trace it, and leaving so large *a part of the whole theory of de- 

 scent a matter of conjecture, that it was easy for those so disposed 

 to point out unanswerable objections. But once admit the facts of 

 ontogenesis, and miracle alone, and this of the most incredible kind, 

 is the only alternative to the acceptance of the fundamental law, 

 which, candidly viewed in the light of these facts, bears every mark 

 of inherent probability. Not only does this law fill out numerous 

 voids and supply many wholly " missing links" in the phylogenetic 

 chain, but it also confirms, in the most remarkable manner, nearly 

 every item of the evidence furnished by the other sources of proof 

 of the doctrine of descent. 



Great, indeed, was the step which this doctrine took when the 

 remarkable revelation was made in the domain of comparative an- 

 atomy, that the Amphioxus possessed a chorda dorsalis, and that 

 the Ascidian larva contained an even more distinct trace or rudi- 

 ment of a vertebral column. Professional naturalists, without pre- 

 conceived ideas could no longer resist the inference that here was 

 the true nexus between the worms and the vertebrates. Consider 

 now, the almost crucial verification which this hypothesis received 

 when it was found that the embryonic stages of every creature 

 higher in the scale of being than the Amphioxus presents phases 

 identical with those of that animal and of the Ascidiae, that even 

 the human embryo has its worm-stage immediately succeeded by 

 its Chordonium stage, and this again by its Acranial stage ; the 

 collateral proofs extending even to the germinative layers, and thus 

 rendering the correspondence complete and the inference irresist- 

 ible. Equally pointed illustrations might be drawn from many 

 other points along the line of common descent. 



But valuable as is this class of evidence at these comparatively 

 advanced stages, it is still more so far down toward the dawn of 



