Page:Popular Science Monthly Volume 43.djvu/647

Rh with a decrease of vital energy, especially if we take into account the permanent white colors of domesticated animals in arctic regions (such, as the Yakutsk horse), which can not be dependent upon natural selection? Some recent observations give a certain support to this supposition. Thus we now learn that rabbits which have been taken to the Pic du Midi Observatory (9,500 feet above the sea level) have given in seven years a race somewhat different from their congeners in the surrounding plains. They are a little smaller, have less developed ears, and their fur coats are of a lighter color and very thick. Moreover, the very consistence of their blood has undergone a notable change. It contains more iron, and possesses a greater power of absorption for oxygen. An anatomical change is thus produced by the environment; and no naturalist will doubt that, if the race continues to multiply for a great number of years in the same conditions, it will maintain its present characters or develop new ones on the same lines, the more rapidly so if natural selection eliminates the less adapted individuals.

A few more additions in the same direction may be found in a valuable work recently published by F. E. Beddard. Thus, he mentions the researches of Dr. Eisig, who has endeavored to explain the ground colors of some animals as dependent upon their food, and has shown, for instance, that the yellow color of an annelid which is living on a yellow marine sponge (a color which might be explained as protective for the parasite) depends upon the yellow pigment of the sponge absorbed by the annelid. The prevalence of crimson colors among some fishes in a certain part of the New England coast, which is covered with scarlet and crimson seaweeds, is explained by J. Browne Goode by the red pigment derived by the crustaceans from the algæ with which their stomachs are full, the crustaceans being devoured by the fishes. And the experiments of Mr. Guyson relative to the effects of different food plants upon a number of species of moths, as well as those of Mr. J. Tawell upon important modifications produced by food in the larvæ of the large tortoise-shell butterfly, both mentioned in the same work, are attempts in a most important but very young branch of experimental morphology.

Another series of researches is now being made with the view of more deeply penetrating into the physiological causes of animal coloration. Thus, it is a fact well known to fishermen, and now