Coleopterological Notices, III. 63 



constancy in the form and size of the rudimentary hind wing, the 

 extreme variation not amounting to more than one-fifth of the 

 average length, the latter being a little more than one-half the total 

 length of the elytra. This is not put forward as proof of any 

 general rule, but simply as an isolated fact in a field very little 

 explored and still less understood. 



It seems extremely difficult to account for this constancy by 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 rudimentaiy organs are not necessarily inordinately variable, 

 and, when comparatively constant, that the standard is maintained 

 by the action of other laws less easily appreciated. 



Darwin, in his "Natural Selection," dwells but briefly upon this 

 question, but gives as one instance of variability in rudimentary 

 organs, the wings of a certain beetle which may be either fully 

 developed or more or less rudimentary. Other authors have also 

 cited examples of a corresponding nature. I think, however, that 

 there is more or less doubt to be attached to this entire category of 

 observations, due to a lack of knowledge of the physical conditions 

 under which the various specimens may have existed. It would for 

 example be manifestly repugnant to the fundamental idea of natural 

 selection to imagine individuals of the same species, with fully 

 developed and rudimentary wings living together on the same 

 bush — except in cases of sexual dimorphism, which constitute a 

 wholly different branch of the subject, — for this very principle 

 would tend to eliminate those individuals which were least able to 

 maintain themselves, and we cannot assume that perfectly and 

 partially developed wings constitute conditions equally fitting the 

 species to maintain itself against a great variety of external influ- 

 ences. 



The only conceivable circumstances under which individuals of a 

 wingless species may, under the same conditions, also be found with 

 more or less developed wings, are due to occasional reversion to the 

 conditions characterizing the primitive stock from which the species 

 may have been derived. If the species has been differentiated for 

 a comparatively great length of time, which may perhaps be judged 

 of approximately by its degree of departure from related winged 

 species, this reversion will surely be quite exceptional. 



Wingless species occurring on oceanic islands are frequently said 

 to be identical with continental fully winged forms, but it seems as 



