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He found that animals of the same class of the animal kingdom showed very similar temperature values, those from the Amphibia examined being 38.5° C., Fishes 39°, Reptilia 45°, and various Molluscs 46°. Also in the case of Pelagic animals he showed a relation between death temperature and the quantity of solid constituents of the body, Cestus having lowest death temperature and least amount of solids in its body.
As a matter of fact, the characters of the two classes are so far united in the Dipneusts that the answer to the question depends entirely on the definition we give of "fish" and "amphibian." In habits they are true amphibia. During the tropical winter, in the rainy season, they swim in the water like the fishes, and breathe water by gills.
Then come the amphibia, which include the toads, frogs, etc. Then come the reptiles, which include the serpents, lizards, crocodiles, turtles, etc. Then come the great family of birds, with its wonderful variety of forms, sizes, and characteristics.
But finally a firm backbone and skull were attained. The appendages. Of these we can say but little. The fish has oar-like fins, attached to the body by a joint, but themselves unjointed. By the amphibia legs, with the same regions as our own and with five toes, have already appeared.
On the whole, I am disposed to think that the direct stem of ascent from the Monorhina to the Amphibia is formed by the Ganoids and the Mudfishes; while the Osseous fishes and the Sharks are branches in different directions from this stem.
The reasons for these facts seem to be that the members of the three orders exemplified have evolved from the same stock, which accounts for their embryonic similarity for a long time after they collectively come to differ from amphibia and reptiles, while the members in each order became differentiated only later, wherefore their embryonic paths coincide for a longer period.
I take it to be certain that Labyrinthodont Amphibia existed in the distributional province which included the dry land depressed during the Carboniferous epoch; and I conceive that, in some other distributional provinces of that day, which remained in the condition of stationary or of increasing dry land, the various types of the terrestrial Sauropsida and of the Mammalia were gradually developing.
The Plesiosauria those extinct marine reptiles of the Secondary period, with long necks, small heads, and paddle-like limbs are of yet higher organization than are the efts and other Amphibia. Nevertheless they present us with a similarity of structure between the fore and hind limb, which is so great as almost to be identity.
In a second order of the salamanders the gills are lost in the metamorphosis, and when fully grown they have only pulmonary respiration. In this fish-like condition they reach sexual maturity, and remain throughout life at the lower stage of the gilled Amphibia. It was formerly regarded as a permanent gilled amphibian persisting throughout life at the fish-stage.
They are still taken on the Lobos Islands, where the provident government of Montevideo restrict the fishery, or hunting, within certain limits, which insures an annual return of the seals. At certain seasons, these amphibia, for the purpose of renewing their coat, come up on the dark frowning rocks and precipices, where there is not a trace of vegetation.
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