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Seeing that a few members of such water-breathing classes as the Crustacea and Mollusca are adapted to live on the land, and seeing that we have flying birds and mammals, flying insects of the most diversified types, and formerly had flying reptiles, it is conceivable that flying-fish, which now glide far through the air, slightly rising and turning by the aid of their fluttering fins, might have been modified into perfectly winged animals.
He reached, by strenuous efforts, the surface of the water, opened his mouth and breathed the air. But for his unfortunate accident, it is probable that the transformation from a water-breathing to an air-breathing animal would have accomplished itself imperceptibly.
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.
Seeing that a few members of such water-breathing classes as the Crustacea and Mollusca are adapted to live on the land; and seeing that we have flying birds and mammals, flying insects of the most diversified types, and formerly had flying reptiles, it is conceivable that flying-fish, which now glide far through the air, slightly rising and turning by the aid of their fluttering fins, might have been modified into perfectly winged animals.
Seeing that a few members of such water-breathing classes as the Crustacea and Mollusca are adapted to live on the land; and seeing that we have flying birds and mammals, flying insects of the most diversified types, and formerly had flying reptiles, it is conceivable that flying-fish, which now glide far through the air, slightly rising and turning by the aid of their fluttering fins, might have been modified into perfectly winged animals.
There is no greater miracle in the world than to see one of these aquatic, water-breathing, limbless creatures transform before your eyes into a terrestrial, four-legged frog or toad, breathing air like ourselves.
Ceratodus is particularly interesting on account of the primitive build of its skeleton; the cartilaginous skeleton of its two pairs of fins, for instance, has still the original form of a bi-serial or feathered leaf, and was on that account described by Gegenbaur as a "primitive fin-skeleton." At the same time the gills also are developed as water-breathing organs in all these lung-fishes.
In two of these families, which were more especially examined by Muller, and which are nearly related to each other, the species agree most closely in all important characters: namely in their sense organs, circulating systems, in the position of the tufts of hair within their complex stomachs, and lastly in the whole structure of the water-breathing branchiae, even to the microscopical hooks by which they are cleansed.
The trampled and sodden straw will rot only to enter into a new life; and I shall pass through a fresh cycle of strange adventures, age after age, till time shall be no more; doing my work in my generation, and fulfilling to the last the will of God, as faithfully as when I was the water-breathing sponge in the abysses of the old chalk sea."
One of the most salient characteristics of the Amniotes is the complete loss of the gills. The Protamniote itself must have entirely abandoned water-breathing. But we do not find in the embryos of the Amniotes any trace of gill-leaves, or of real respiratory organs on the gill-arches. It is very probable that the urinary bladder of the Dipneusts is the first structure of the allantois.
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