a minute replica of the adult which formed it, a multum in 

 parvo which simply unfolded and enlarged to produce an- 

 other adult organism ; Wolff, however, showed that this 

 view lacked a basis in fact, and that as we now universally 

 believe, embryonic history is a true development from the 

 simple and unorganized to the progressively more and 

 more specialized later conditions, that it is, in a word, an 

 epigenesis. The great name of the infancy of embryology 

 is that of Von Baer ( 1792-1876) . This acute observer and 

 thinker was struck by the similarity of early stages in the 

 development of quite different adult animals. Birds and 

 reptiles and even mammals pass through stages when they 

 possess gill-slits like those of fishes, related to heart and 

 blood-vessels like the similar structures in lower verte- 

 brates ; butterflies and flies and beetles are somewhat alike 

 in their larval stages, when as caterpillars and maggots and 

 grubs they not only resemble one another remarkably but 

 they are also very like worms. Under the influence of the 

 evolution doctrine, then becoming more generally accepted, 

 Von Baer and a host of followers extended the science of 

 comparative embryology until Haeckel in 1866 ventured to 

 state the "Law of Recapitulation," or the "Biogenetic 

 Law," in the following rigid terms: Ontogeny recapitu- 

 lates Phylogeny. (The development of an individual re- 

 views the past history of its species. ) Led by their enthu- 

 siasm many of the later nineteenth century zoologists fol- 

 lowed too implicitly the lines of the embryonic record, 

 though Haeckel himself, the most radical advocate of the 

 law, pointed out that there are many serious omissions in 

 the narrative, that false passages are inserted as the result 

 of purely larval and embryonic needs and adaptations, 

 while many alterations in the way of anachronisms have 

 been made. Of late years there has been a strong reaction 

 from the complete acceptance of the principle as a reliable 

 mode of interpreting embryonic histories. But I believe 



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