Page:Popular Science Monthly Volume 10.djvu/24

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Prof. N. S. Shaler[1] on the connection between the development of the life and the physical conditions of the several continents, showing first that the greatest amount of shore-line in proportion to the internal areas indicates a greater diversity of surface within.

Another proposition he attempts to establish: that in proportion to the shortness of the shore-lines, or, in other words, to the want of variety in their surfaces, will be the diversity of animal life in the continent. He then proceeds from Darwin's standpoint, and follows out many curious and instructive lines of thought regarding increased amount of influences in diversified surfaces—a level plain having the same conditions throughout, but a mountainous region having for each one thousand feet of elevation a new condition of things, in the form of streams, winds, humidity, and the like. In areas of simple outline and unvarying surfaces we do, in fact, have a less diversity of forms.

Recognizing the mutation of continents through past geologic ages, we again see the accompanying physical changes in not only modifying forms, but in selecting them afterward by succeeding changes.

The widely-diversified nature of the facts bearing on the doctrine of natural selection baffles all attempts at a systematic classification of them. Of such a nature are many of the valuable communications of Prof. Wilder.

At the meeting of this Association[2] he has, among other matters, confirmed in a young lion the discovery of Prof. Flowers that, in the young dog and probably in other carnivora as well, the scapho-lunar bone has at the outset three centres of ossification, and that these really represent the radiale intermedium and centrale of the typical carpus. By study of a fœtal manatee, Prof. Wilder is able to determine its affinities, and to point out the probable retrograde metamorphosis of some ancient ungulate animal, and that the manatee is widely removed from the whales with which it has been associated.

Mr. William K. Brooks has published a very remarkable paper on certain free swimming tunicates, the Salpa, giving for the first time a clear and comprehensive history of certain obscure points, and has at the same time applied the principles of natural selection theoretically in showing the origin of salpa from sessile tunicates, and making clear the peculiar modification of parts which accompany these changes.

In the field of entomology some capital work has been done, both practical and theoretical.

Prof. Riley's demonstration of the yucca-moth is unique in its way. Dr. Engelmann has discovered that the yucca depends upon insects for fertilization; and Prof. Riley, by patient study, not only

  1. "Proceedings of the American Academy," vol. viii., p. 349.
  2. "Proceedings of the American Academy of Arts and Sciences," vol. xxii., p. 301.