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.
AMPHIBIA, a zoological term originally employed by Linnaeus to denote a class of the Animal Kingdom comprising crocodiles, lizards and salamanders, snakes and Caeciliae, tortoises and turtles and frogs; to which, in the later editions of the Systema N aturae he added some groups of fishes.
In addition Cuvier accepts the Linnaean subdivisions of Amphibia-Reptilia for the tortoises, lizards (including crocodiles), salamanders and frogs; and Amphibia-Serpentes for the snakes, apodal lizards and Caeciliae.
In 1799' Alexandre Brongniart pointed out the Wide differences which separate the frogs and salamanders (which he terms Batrachia) from the other reptiles; and in 1804 P. A.
Salamanders, toads and frogs are numerous, and crocodiles abound.
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