Open main menu

Page:Popular Science Monthly Volume 32.djvu/111

This page has been proofread, but needs to be validated.
101
AMERICAN ZOÖLOGISTS AND EVOLUTION.

eggs are less in number and smaller in size.[1] Mr. Robert Ridgway[2] calls attention to the geographical variation observed in Dendræca.

The same author,[3] in a discussion of a paper by Salvin in the "Transactions of the Zoölogical Society of London," on the relationships between the birds of Guadeloupe and the mainland, refers to the present genesis of species, and points to the increase in size of the bill and feet, the shorter tail and wings and darker colors, as characterizing them.

Dr. E. C. Coues,[4] in his studies regarding geographical variation in color among North American insectivorous mammals, says: "My studies up to the present go to show a very interesting parallelism with the state of the case I have determined for other small mammals, notably the mice and gophers, and which my friend Mr. Allen has admirably brought out in his studies of the squirrels. In some cases I find almost identical effects of climatic or other conditions upon the shrews and the mice of particular localities, by which they both acquire the same facies loci. Present indications are that the normal variability of the shrews in size, shape, and color is not less than has been determined to hold good in various other families of mammals." In this memoir Dr. Coues has verified a curious fact, first pointed out by Professor Baird, of the modifications of the premolar dentition which the Western species collectively, as compared with the Eastern, have undergone: "A striking peculiarity of all the Western species, no matter how diverse in other respects, is to have the 'third premolar' decidedly smaller than the 'fourth,' while in all the species east of the Rocky Mountains (with one possible exception) the same tooth is as large as, or larger than, the other. Of the fact there is no question; it may be observed in an instant, and is unmistakable. Its significance is another thing. Some of the Western species are scarcely distinguishable if at all from their respective Eastern analogues, except by this character, and they all show it."

Professor A. Hyatt[5] finds in sponges geographical variation in color, referring to similar features in birds as recorded by Baird and others.

Professor David S. Jordan,[6] in a paper on the distribution of freshwater fishes, presents a concise series of propositions which govern these animals in the United States. They all point to the action and importance of physical conditions as governing distribution. Space will permit only the quoting of the last proposition, which is a summing up of his conclusions: "The distribution of fresh-water fishes

  1. "Bulletin of the Nuttall Ornithological Club," vol. i, p. 74.
  2. Ibid., p. 81.
  3. Ibid., vol. ii, p. 58.
  4. "Bulletin of the United States Geological Survey of the Territories," vol. iii. No. 3, p. 635.
  5. "Memoirs of the British Society of Natural History," vol. ii, part iv.
  6. "American Naturalist," vol. xi, p. 607.