I0 2 NORTH AMERICAN DIPTERA. 



Probably we shall yet learn of other mosquitoes which 

 are culprits in these respects. 



This gravely important bearing of the mosquitoes in 

 man's economy has given a tremendous impulse to their 

 study, though not always w 7 ith the most happy results so 

 far as their taxonomy is concerned. Whereas ten or 

 twelve years ago only about one hundred and fifty spe- 

 cies of the family were known, we now have an accred- 

 ited list of Culicidse of nearly or quite six hundred spe- 

 cies, and there are probably several hundred more yet 

 awaiting discovery. 



It seems a fact that the mosquitoes present but few and 

 slight structural differences among themselves ; the many 

 closely related forms seem to indicate a late geological 

 crudescence. Such organisms are always difficult to 

 classify. The wing venation has acquired much fixity, 

 whereas the many secondary sexual differences in the 

 mouth-organs would indicate a late adaptation to blood- 

 sucking habits. The Culicinse probably have developed 

 from the corethrine type, which is doubtless an older 

 type, now decidedly on the wane. Until within a few 

 years scarcely a half dozen genera of the mosquitoes had 

 been recognized by dipterologists, and they were based 

 chiefly on the secondary sexual mouth characters. Within 

 these few years, however, the numerous writers 011 this 

 group of insects have proposed fully one hundred gen- 

 era, for the most part merely subdivisions of the older 

 genera, founded on minor characters, chiefly the shape 

 and arrangement of the scales of the body and wings. It 

 seems to be the consensus of opinion among other dipter- 

 ologists that the use of such characters has been car- 

 ried to an undue and even absurd extreme. Of course 

 the first requisite in classification is that distinguishing 

 characters shall be 'natural', that is genetic, not homo- 

 plastic or parallel characters. When such are found it 



