352 



CHARLES T. BRUKS. 



they differ from those of the more specialized Brachycera like the 

 Muscidea only in their more strongly developed bristles. 



It is in the venation of the wings that the Phorida; depart most 

 strikingly from the other Diptera. This varies among the few 

 known genera only in trivial details, so that the general type for 

 the entire family is practically uniform. Fig. 3 shows the wing 

 of a typical species. The veins can at once be divided into two 

 groups, the several heavy ones which lie close together at the 



FIG. 2. Commoptera solcnop- FIG. 3. Diagrammatic Phorid Wing. 



sidis Brues, mouthparts of 9 (After Becker. ) 



basal half of the wing anteriorly, and the four delicate ones which 

 pursue an oblique course across the posterior part of the wing. 

 This arrangement is so peculiar, that attempts to homologize the 

 veins with those of other Diptera have proved very unsatisfactory. 

 Several families present a somewhat similar appearance and in 

 each case comparisons have been drawn. Williston, in the paper 

 referred to above ('06) mentions the close similarity in venation 

 to the Bibionicl genus Apistes, and Becker ('01) earlier noted the 

 resemblance to Scatopse another member of the Bibionidae and to 

 Siuinliuin belonging to the Simuliidae. It is true that there is a 

 close superficial resemblance but no attempt has been made to 

 homologize the veins. It is evident that Apistes, Scatopse and 

 Siniulium are all considerably specialized and we can indeed trace 

 through the Bibionidse the loss of the posterior series of veins 

 which are quite strong in Bibio, weaker in Diloplius and still more 

 so in Scatopse and Apistes, with a coincident strengthening of 

 the anterior veins and their withdrawal basally. That a resem- 

 blance between this, the result of specialization within a family of 

 closely similar forms and another otherwise widely different family 



