reptiles of the Tartar and Arabian deserts, the Great Sahara, and the sands of Arizona and California. There is also a tendency to produce spiny forms in Such places; witness the Stellios and Uromastix and Cerastes of the Sahara, the Phrysonomas and Horned Rattlesnake of Southwestern America. The vegetation of every order, we are also informed, is in these situations extremely liable to produce spines and thorns."
Every one is aware of the great difference in size and color exhibited by the male and female of birds, butterflies, etc., of male animals being armed with weapons, like the horns of deer, the cock's comb, etc. Mr. Darwin supposes these organs to have arisen through what he calls Sexual Selection. Thus, at breeding-time the number of male deer exceeds that of the female; hence there is invariably a fight, and the deer with the biggest horns gets the better of his rivals: naturally their posterity will be characterized by large horns. This process, continued through generations, finally results in the production of the antlers of the male deer. But, as Mr. Herbert Spencer observes, large horns require large muscles to move the head, large muscles must be supplied with sufficient nutriment, which is brought to them by large arteries, which necessitates a powerful heart, and so on indefinitely. The voice of the singing birds is supposed to have arisen in the same way, for of the male birds those who sing best are chosen by the females for their mates. The voice is therefore continually improved from generation to generation. The male Crickets, Grasshoppers, Katydids are equally remarkable for the noise they can make. The incessant "Katydid she didn't" is produced by one wing being played on by the other wing, like a fiddle and bow. "All observers agree that the sounds serve either to call or excite the mute females;" and Mr. Darwin quotes Mr. Bates as stating that the male of the European field-cricket "has been observed
