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Updated: July 27, 2025
At the same time each species of the Cervidae has its special characters in the antlers, in shape and branching, and it would be impossible to attribute these to differences in mode of fighting: they are due to mutation. In connexion with the metamorphosis of Amphibia the case of the Axolotl has always been of very great interest.
But even the existing Amphibia have such important relations to us in their anatomic structure, and especially their embryonic development, that we may say: Between the Dipneusts and the Amniotes there was a series of extinct intermediate forms which we should certainly class with the Amphibia if we had them before us.
The Teleostei are modified Ganoidei. The Dipneusta gave rise to the Amphibia, which are the root of all other Vertebrata, inasmuch as out of them were developed the first Vertebrata provided with an amnion, or the Protamniota. The Protamniota split up into two stems, one that of the Mammalia, the other common to Reptilia and Aves.
The great interest of the natural history of the Amphibia consists especially in their intermediate position between the lower and higher Vertebrates. The lower Amphibia approach very closely to the Dipneusta in their whole organisation, live mainly in the water, and breathe by gills; but the higher Amphibia are just as close to the Amniotes, live mainly on land, and breathe by lungs.
Then the flat worms and mollusks took to a creeping mode of life, while the annelids and vertebrates still swam. Then the annelids settled to the bottom and crept, and all their descendants remained creeping forms. The vertebrates alone remained swimming, and probably neither they nor their descendants ever crept until they emerged on the land, or as amphibia were preparing for land life.
The cerebellum increases with the greater locomotive powers of the animal. But its development is evidently limited. The large brain, or cerebrum, is in fish hardly as heavy as the mid-brain; in amphibia the reverse is true. In higher recent reptiles the cerebrum would somewhat outweigh all the other portions of the brain put together.
In these the floating bladder has turned into lungs, and the air-passage into a trachea. The lungs of the Amphibia have been transmitted to the three higher classes of Vertebrates. In the lowest Amphibia the lungs on either side are still very simple transparent sacs with thin walls, as in the common water-salamander, the Triton. It still entirely resembles the floating bladder of the fishes.
Among the important changes of the vertebrate organisation that marked the rise of the first Amniotes from salamandrine Amphibia during this period the following three are especially noteworthy: the entire disappearance of the water-breathing gills and the conversion of the gill-arches into other organs, the formation of the allantois or primitive urinary sac, and the development of the amnion.
When the skeletons of fishes of the Ceratodus type were discovered in the Devonian rocks, it was felt that we had found the fish-ancestor of the land Vertebrates, but a closer anatomical examination has made this doubtful. The Devonian lung-fish has characters which do not seem to lead on to the Amphibia.
No vertebrated animals more highly organised than fish were known in rocks of higher antiquity than the Permian until the year 1844, when the Apateon pedestris, Meyer, was discovered in the coal-measures of Munster-Appel in Rhenish Bavaria, and three years later, in 1847, Professor von Dechen found three other distinct species of the same family of Amphibia in the Saarbruck coal-field above alluded to.
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