298 THE ZOOLOGIST. 



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 tempera- 

 ture "* under which the eggs have been matured. A fuller know- 

 ledge of these Phasmidce will scarcely support this proposition. 

 What we find is a most graduated and complicated connection 

 between the winged and wingless forms. The late Prof. West- 

 wood, 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.f 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 antennae and very attenuated 

 bodies, and progresses to those having long setiform antennae, 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 



* Prof. Semper's definition of the " optimum temperature" seems to be 

 contained in the following sentence: — "The interval between the daily 

 extremes may be great or small without any alteration in the daily meteor- 

 ological mean ; moreover, the favourable temperature — the optimum of 

 temperature for the animal — may either coincide with the meteorological 

 mean, or lie nearer to one of the extremes — the maximum or minimum — 

 than the other." 



f ' Catalogue of Orthopterain the Brit. Museum's Coll.' Pt. i. Phasmidce 

 (1859). 



