46 Journal New York Entomological Society. [Vol. xvi. 



several groups of insects in which we find a degeneration of the wings. 

 All the higher groups of insects are normally winged, but there are 

 here and there a few restricted groups which have developed genera 

 or species that are partially, almost, or even completely apterous. 



In a former paper (The Structure and Significance of Vestigial 

 Wings among Insects, Biol. Bull., Vol. 4, pp. 179-190) I have pre- 

 sented very briefly some more general conclusions concerning insects 

 with vestigial wings. The present one deals only with a few special 

 cases which seem to have some bearing on the principles of natural 

 selection and mutation as applied to the evolution of these organs. 



The all-sufficiency of natural selection to explain the origin of all 

 wingless insects was granted by Darwin, and has been accepted by 

 later investigators with an occasional slight protest. Thus, in 189 1 

 Casey (Ann. N. Y. Acad. Sci., Vol. 6, p. 65) referring to the con- 

 stancy of vestigial wings says : 



" It seems extremely difficult to account for this constancy on the 

 theory of natural selection, and, as it is impossible to doubt the ever- 

 acting reality of the principle in question, we can only infer that rudi- 

 mentary vestigial organs are not necessarily inordinately variable, and 

 when comparatively constant, that the standard is maintained by the 

 action of other laws less easily appreciated." 



That we cannot hope to explain all cases of this sort by natural 

 selection alone, I am firmly convinced from the few groups that I 

 have examined. This is especially true of many genera of partially 

 wingless beetles where the wings are protected beneath a sheath com- 

 posed of the fused and immovable elytra. Thus enclosed between the 

 wing covers and the body they are entirely without influence either 

 physiologically on the animal itself, or externally in relation to its 

 environment. Yet, under these conditions, we find them to be 

 remarkably constant specific characters although not at all uniform 

 within the range of many of the genera. 



Several of the cases to be noted in the sequel point very strongly 

 toward the occurrence of mutations in the origin of vestigial wings, 

 while others, so far as I can see, require the assumption of distinctly 

 orthogenetic or determinate tendencies in the degeneration of these 

 structures. 



The coleopterous family Carabidae furnishes numerous interesting 

 cases of wing degeneration which are in strong contrast to the well- 

 developed condition of the wings among the majority of the family. 



