6 14 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 de- 

 gree 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 verte- 

 brate 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 retro- 

 gressive development has been more general in early geological pe- 

 riods, 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. 



Br Db. 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 



