Page:Popular Science Monthly Volume 10.djvu/16

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6
THE POPULAR SCIENCE MONTHLY.

the generic lists of to-day! In an article on the "Proteus of Lake Erie," he expressed his aversion to multiplying names in zoölogy, and lamented the tendency. He protested as follows, fifty years ago: "By some, these innovations have been so wantonly introduced, as almost to threaten in the end the erection of every species into a distinct genus."[1] Though these words were undoubtedly aimed at Rafinesque, they were none the less prophetic. Whatever may be said of the existence in nature, of other groups, there can be no question that species have the most definite existence, and it would seem then that nothing more need be proved for the theory of descent as opposed to the theory of special creation, than the establishment of the fact that species assume the characters of new species, or disappear altogether with a change of surroundings. As examples might be cited, the transplanting of Alpine seeds to warmer regions below, and an accompanying change of the plant into another species before known in the warmer region, or, more remarkable still, the change of a species of Crustacean which lives in salt water, to another species with a partial freshening of the water, and this freshening slowly persisted in, the form changing into another genus, and in so doing losing: one of its segments. In the first case we see the effect of temperature, and in the second case the physical influence of salt and water in different proportions.

Now, these and hundreds of similar examples can be incontestably proved.

Even the prolonged existence of the form of some animals, like Lingula, may be referred to an inherent vitality which enables them to survive changes that caused the death of thousands of others.

In an early discussion of Darwin's theory,[2] Prof. Agassiz cited the persistence of Lingula as fatal to the theory, and Prof. William B. Rogers replied that the vital characters of some animals would enable them to survive above others. Ten years later, I had an opportunity of studying living Lingula on the coast of North Carolina, and brought specimens home alive in a small jar of water, and kept them in a common bowl for six months without the slightest care. Their power of surviving under changed conditions—their vitality, in other words—seems incredible.[3] (For further details, see reference below.)

It has for a long time been suspected that the species of Mollusca, described in such profusion in this country, would be reduced when the slightest attention to their habits had been made. Dr. James Lewis[4] long ago observed that a certain species of fresh-water mussel, described as Alasmodonta truncata, is only the truncate form of another species, A. marginata. From a careful study of the condi-

  1. American Journal of Science and Arts, vol. vii., 1829.
  2. "Proceedings of the Boston Society of Natural History," vol. vii., p. 231, December 15, 1860.
  3. Ibid., vol. xv., p. 315.
  4. Ibid., vol. v., p. 121.