THE STRUCTURE AND SIGNIFICANCE OF VES- 

 TIGIAL WINGS AMONG INSECTS. 



CHARLES T. BRUES. 



Although considerable attention has been paid by entomolo- 

 gists to the structure and development of the wings of insects, 

 but few observers have ever given any careful descriptions of in- 

 sect wings which are in a vestigial condition. The well-marked 

 constancy of the wing structure and its use as an aid to classifi- 

 cation has long been recognized, so that one can not fail to sus- 

 pect a priori that there should be a considerable range of vari- 

 ation in the structure of vestigial l wings. That the wings are 

 exceedingly important organs has never been questioned, indeed, 

 it is a generally accepted view that they are one of the most im- 

 portant factors in making the Insecta such a dominant group, 

 and the causes which 'induce their atrophy must undoubtedly be 

 deep-seated. Moreover, from the extent of degeneration it should 

 be possible to obtain some knowledge as to the length of time 

 during which such causes may have been acting. How far such 

 a method may be relied upon, it is my present desire to show. 



In a recent paper upon the reduction of wings among the 

 Diptera Bezzi ('oo) has shown thaj there are two categories into 

 which we may divide such Diptera accordingly to the apparent 

 cause of the wingless condition, viz.: First, cases brought about 

 by external parasitism. Second, those induced by a secluded 

 environment: It is possible to include almost all the general 

 types of wingless insects under these two heads, except in a few 

 cases where other influences seem to be at work. 



The examination of a number of myrmecophilous Hymenop- 

 tera and Diptera has called my attention to the fact that several 

 rather clearly defined types of vestigial wing structure may be 



1 The term vestigial is here used instead of rudimentary. The latter word has 

 often been employed in this connection by entomologists, but with evident impropriety, 

 as it should apply in its strict sense only to organs still in process of ontogenetic de- 

 velopment. 



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