Page:The Zoologist, 4th series, vol 3 (1899).djvu/324

298 harmony with their surroundings, and thus coming under the sanction and perpetuating influence of natural selection. On this theory the Stick-insect would be merely the survival of an ancient "Larva-form" which fulfilled the same purpose, and thus also came down to us unchanged under the fostering care of the same selective influence. But Prof. Semper, further speculating on the fact of these insects comprising winged and wingless forms, is inclined to account for the same by the "optimum temperature" under which the eggs have been matured. A fuller knowledge of these Phasmidæ will scarcely support this proposition. What we find is a most graduated and complicated connection between the winged and wingless forms. The late Prof. Westwood, a most determined opponent to evolution in any shape or form, contributed—as so many other opponents have done before and since—unconscious testimony to the same, in an artificial classification which he proposed for the family. As summarized by Mr. Bates:—"The groundwork of this classification is the gradation or development of the wings from genus to genus. Thus it begins with those genera which are wingless in both sexes, these forming one Division, and passes through those in which the males are winged and the females wingless, or in which the wings are rudimentary, to the genera which have well-formed wings in both sexes—the whole of the latter forming the second Division. The wingless series commences with those forms which have much abbreviated antennæ and very attenuated bodies, and progresses to those having long setiform antennæ, or bodies of much more compact structure. The winged series progresses gradually from those genera in which the upper and lower wings are either rudimentary, or developed in one sex only, to those in which they exist in both sexes (but the upper wings of extreme shortness), ending at length with genera in