Page:Popular Science Monthly Volume 68.djvu/506

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502

POPULAR SCIENCE MONTHLY

with the upper jaw produced into a flat blade. In numerous unrelated groups of fishes, she has produced genera with the parrot's beak (Scarus, Oplegnathus, Tetraodon), or with an imitation of human incisors. In many different wholly unrelated groups she has developed bony plates, hardly to be distinguished superficially from those of her ancient ostracophores and dipnoans. Thus the earlier writers placed with the ganoids such forms as Callichthys, Ostracion, Agonus, Pegasus, Hippocampus, Gasterosteus, Peristedion, forms now known to have no affinities with the extinct mailed fishes, and for the most part no affinities with each other.

Such adaptive characters do not suggest relationship. They are mostly superficial only, and indicate not the origin or affinities of the forms possessing them, but rather the habits of the species in question, and the needs of their recent environment.

In finding what an animal really is, that is, in tracing its ancestry, we have in the words of Haeckel, mainly the three ancestral documents, morphology, embryology and paleontology. Adaptive characters are essentially external. The inside of an animal tells what it is, the outside where its ancestors have been. Perhaps a fuller understanding of orthogenesis will relate its facts to those of 'analogous variation' or the 'convergence of characters' in unrelated forms.