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THE POPULAR SCIENCE MONTHLY.

than any of the other divisions of vertebrata. And paleontology and zoology show that they have pursued a course which is in its essential principle the same as that displayed by the Batrachia, and in a less degree by the Reptilia. They have diverged further and further away from the batrachians, which they once resembled, and in so doing have left behind them the general ascending line that led some of the land animals to become Mammalia. They have become specialized into types which have special modes of life adapted to special localities. Some of the lines of descent are clearly degenerate, as indicated by a loss of parts. Some of these degenerate lines inhabit the deep sea; others have become movably sessile, attaching themselves to fixed bodies. Others have found protection in an external armor of bony plates rather than in activity and sensibility. But many fishes are in their especial way wonderful exemplars of animal energy, though none of them rise high in the scale of intelligence.

In review of the results obtained from the recent study of vertebrate paleontology, certain principles may be clearly discerned. These are as follows: 1. The earlier types were more generalized, the later ones more specialized. 2. The specialization is sometimes upward or progressive, and sometimes downward or retrogressive. 3. The retrogressive development has been more general in early geological periods, the progressive more general in the later geological periods. For a more detailed exposition of these principles, see "American Naturalist" for February, March, and April, 1885.

It is not my intention in this article to do more than to display the facts of the case. The exposition of the hypotheses of evolution which explain these facts must be reserved for another article. Suffice it to say here, that the study of the changes of structure displayed by the lines of evolution, has brought to light some very definite exhibitions of the application of energy. The illustration of the modus operandi of this creative energy is a very important chapter of evolution, and one that interests mankind practically, even more than as food for his intellectual activity.

 

AN EXPERIMENT IN PRIMARY EDUCATION.
By Dr. MARY PUTNAM-JACOBI.
II.

ONLY one attempt was made during this year to teach the child the meaning of words. It was done through a simple generalization which had become indispensable in the study of geometry, when she passed from plane to solid figures. By means of wooden models she learned, in addition to the cube—the sphere, ovoid, oblate, cylinder, prism, tetrahedron, octahedron, and dodecahedron. She then was led