In a remarkable essay 3 Meckel remarks: ' ` There is no good physiologist who has not been struck by the observation that the original form of all organisms is one and the 1 " 11 s'agit donc de prouver que la serie qui constitute l'echelle animale reside essentiellement dans la distribution des masses principales qui la composent et non dans celle des especes ni meme touj ours dans celle des genres."
Meckel proceeds to exemplify the thesis, that the lower forms of animals represent stages in the course of the development of the higher, with a large series of illustrations.
After comparing the salamanders and the perenni-branchiate Urodela with the tadpoles and the frogs, and enunciating the law that the more highly any animal is organized the more quickly does it pass through the lower stages, Meckel goes on to say: " From these lowest Vertebrata to the highest, and to the highest forms among these, the comparison between the embryonic conditions of the higher animals and the adult states of the lower can be more completely and thoroughly instituted than if the survey is extended to the Invertebrata, inasmuch as the latter are in many respects constructed upon an altogether too dissimilar type; indeed they often differ from one another far more than the lowest vertebrate does from the highest mammal; yet the following pages will show that the comparison may be also extended to them with interest.
Meckel, "Anatomie des Gehirns der Vogel," in Meckel's Archiv f.
Meckel, 3 on the other hand, while equally accepting Brongniart's classification, retained the term Amphibia in its earlier Linnaean sense; and his example has been generally followed by German writers, as, for instance, by H.
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