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This assures the zoölogist that the origin of the lungs in the higher animals is found in the swim-bladder of the so-called lungfish. In this Silurian time certain of these lungfish were perhaps trapped in the basin in the marsh by the uplifting of the border.
Among bony fish, I noted grizzled wrasse unique to these seas, deep-water gilthead whose iris has a fiery gleam, one-meter croakers whose large mouths bristle with small teeth and which let out thin cries, black rudderfish like those I've already discussed, blue dorados accented with gold and silver, rainbow-hued parrotfish that can rival the loveliest tropical birds in coloring, banded blennies with triangular heads, bluish flounder without scales, toadfish covered with a crosswise yellow band in the shape of a Greek t, swarms of little freckled gobies stippled with brown spots, lungfish with silver heads and yellow tails, various specimens of salmon, mullet with slim figures and a softly glowing radiance that Lacépède dedicated to the memory of his wife, and finally the American cavalla, a handsome fish decorated by every honorary order, bedizened with their every ribbon, frequenting the shores of this great nation where ribbons and orders are held in such low esteem.
Among these fishes were some which bear a great resemblance to a few found in South America, in Africa and Australia to-day, and which we know as lungfish. Anyone who has cleaned our fresh water fishes in preparation for the table will remember that inside of them there is a long slender bladder filled with air.
The simple forms of the life of lowly creatures, as well as the simple character of the legs and feet in the salamander class, make the explanation not so unlikely as would at first sight appear. Suffice it to say that the scientist now believes that out of the lungfish of the Devonian came the amphibians of the Carboniferous period.
To this fact he owes his name of lungfish. We sometimes gain much light concerning the past history of any particular form of animal by studying the development of that animal in the egg, or, in the case of the mammals, before birth.
This bladder assists in making the fish light, hence making it easier for it to support itself in the water. In certain swampy regions these lungfish swim freely in the water of the marshes. When the dry season comes, however, the water evaporates, draining the marshes completely. This would prove the death of most fishes. The lungfish have a curious habit which keeps them over the dry season.
The swim-bladder which we have just described in other fishes is, with this lungfish, peculiarly spongy in its walls, presenting a large surface full of blood vessels which absorb the air on the inside of the bladder. This air the fish changes with moderate frequency, the result being that the swim-bladder serves him exactly as the lung serves a higher animal.
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