Page:Popular Science Monthly Volume 10.djvu/23

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13
AMERICAN ZOÖLOGISTS AND EVOLUTION.

Prof. A. E. Verrill,[1] on the supposed eastern migration of the cliff-swallow, traces historically its first appearance in various places in the East, and is inclined to the opinion that as the country became settled by Europeans the birds left their native haunts for barns and houses, and increased in number to a greater extent than before on account of the protection invariably furnished by man.

Rev. Samuel Lockwood[2] records a curious case of the Baltimore oriole acquiring a taste for the honey-sacs of bees, tearing off the heads of those insects, and, having secured the honey-sacs, rejecting the rest of the body.

Prof. Wyman[3] observes a curious case in Florida of a colt and a number of pigs and cows thrusting their heads under water and feeding on the river-grass, in some cases remaining with their heads immersed for half a minute.

Hon. A. II. Morgan[4] observes the widest difference in the habits of the same species of beaver in the Lake Superior region and in the Missouri, constructing their dams and ways differently, and meeting the varied conditions, not by a blind instinct, but by a definite intelligence manifested for definite purposes.

All of these facts, simple in themselves, yet together go to prove that animals do vary in their habits, and with a persistent change in habits arises the minute and almost insensible pressure to swerve and modify the animal.

So much does the influence of season, with its accompanying peculiarities of food, temperature, humidity, and the like, affect certain animals developing coincidently with its different phases, that it is instructive to note that in certain species of insects two or three different forms occur. Thus Mr. Edwards[5] has in an elaborate way worked up the history of a polymorphic butterfly [Ephiclides ajax), showing that there are three forms heretofore regarded as distinct species, which are only varieties of one and the same species, but appearing at different times of the year, and consequently confronted by different influences as to temperature, moisture, food, and the like. These forms are known under the names of Walshii, Telemonides, and Marcellus, and both sexes are equally affected. The first form mentioned represents the early spring type, Telemonides the late spring type, and Marcellus the summer and autumn type {see also Mr. Scudder's paper[6]). If these influences affect species, we should expect to see the greatest variety of forms in a country possessing the widest diversity of conditions.

Some suggestive paths of investigation have been pointed out by

  1. "Proceedings of the Boston Society of Natural History," vol. ix., p. 276.
  2. American Naturalist, vol. vi., p. 721.
  3. Ibid., vol. viii., p. 237.
  4. "The American Beaver and his Works."
  5. "Butterflies of North America," part ix.
  6. American Naturalist, vol. viii., p. 257.