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The vertebrae were not ossified, for no trace of them has been found. DEVONIAN FISHES. The TRUE FISHES of the Devonian can best be understood by reference to their descendants now living. Modern fishes are divided into several groups: SHARKS and their allies; DIPNOANS; GANOIDS, such as the sturgeon and gar; and TELEOSTS, most common fishes, such as the perch and cod.
In every form man has passed through, he left behind some old member or power and took on some new. He left his air-bladder and his gills and his fins with the fishes; he got his lungs from the dipnoans, the precursors of the amphibians, and from these last he got his four limbs; he left some part of his anatomy with the reptile, and took something in exchange, probably his flexible neck.
They had not evolved into the ferocious monsters which were later to be masters of the seas. DIPNOANS, OR LUNG FISHES. These are represented to-day by a few peculiar fishes and are distinguished by some high structures which ally them with amphibians. An air sac with cellular spaces is connected with the gullet and serves as a rudimentary lung.
On the line of the ancestry of most modern fishes its duct was closed and it became the swim bladder used in flotation and balancing. On another line of descent it was left open, air was swallowed into it, and it developed into the rudimentary lung of the dipnoans and into the more perfect lungs of the amphibians and other air- breathing vertebrates.
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