Fig. 271.—An African Catfish, Chlarias breviceps Boulenger. Congo River. Family Chlariidæ. (After Boulenger.)
Fig. 272.—Silverfin, Notropis whipplii (Girard). White River, Indiana. Family Cyprinidæ.
We have thus seen, in hasty review, that the fish-like vertebrates spring from an unknown and possibly worm-like stock, that from this stock, before it became vertebrate, degenerate branches have fallen off, represented to-day by the Tunicates and Enteropneustans. We have seen that the primitive vertebrate was headless and limbless and without hard parts. The lancelet remains as a possible direct offshoot from it; the cyclostome with brain and skull is a possible derivative from archaic lancelets. The earliest fishes leaving traces in the rocks were mailed ostracophores. From an unknown but possibly lamprey-like stock sprang the 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 Crossopterygians, into Dipnoans, or lung-fishes, and perhaps into Ostracophores. All these types and others abound in the Devonian Age and the early records were lost in the Silurian. From the Crossopterygians or their ancestors or descendants by the specialization of the lung and limbs, the land animals, at first amphibians, after these reptiles, birds, and mammals, arose.
Fig. 273.—Moray, Gymnothorax moringa Bloch. Family Murænidæ Tortugas.
Fig. 274.—Amber-fish, Seriola lalandi (Cuv. & Val.). Family Carangidæ. Woods Hole.
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, herring, mackerel, perch, which culminate in specialized and often degraded types, as the anglers, globefishes, parrot-fishes, and flying gurnards; 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.