lampreys gave rise to sharks and chimæras. The sharks developed into rays in one right line, and into the highest sharks along another; while by a side branch through lost stages the primitive sharks passed into dipnoans or lung-fishes. All these types and others abound in the Devonian age and the early records were lost in the Silurian. From the lung-fishes or the ancestors or descendants by the specialization of the lung and limbs, the land animals, at first amphibians, after these reptiles, birds and mammals, arose.
In the sea, by a line still more direct, through the gradual emphasis of fish-like characters, we find developed the crossopterygians with archaic limbs and after these the ganoids with fish-like limbs but otherwise archaic; then the soft-rayed and finally the spiny-rayed bony fishes which culminate in specialized and often degraded types, as the anglers, globe-fishes, parrot-fishes and flying gurnards. Side branches are the ostracophores, perhaps from primitive lampreys; arthrognaths from a lost ancestry possibly; chimseras, from primitive sharks, and rays from sharks less primitive; dipnoan sturgeons, gar-pikes and perhaps carp and cat-fishes; and from each of the ultimate lines of descent radiate infinite branches till the sea and rivers are filled, and almost every body of water has fishes fitted to its environment.