Vol. 1.] 



Woodivorth. — Wing Veins of Insects. 



131 



FKt. 71. Diagram representing tlie 

 venation in Cecidomyidfe and Myee- 

 tophilida\ Solid lines represent con- 

 stants in Ceoidomyidte : line CM is 

 variable in botli families ; lines M are 

 variable in Mycetophilida?, and en- 

 tirely absent in Ceoidomyidw; the 

 other dotted lines are constant in 

 Mycetophilidic and variable in Ceci- 

 domyidfe. 



The families in which the largest number of veins occur are 

 the Tipulide? and the Psychodida^; the smallest number is 

 found in the Cecidomyidae. These three families are all closely 

 related, and the group to which they belong is, by general 

 consent, placed at the lower end of the series. 



The Cecidomyidfe are very closely related to the Myceto- 

 philidffi. The venation of both 

 families is shown in Fig. 71. 

 With the exception of the vein 

 marked CM, which may disap- 

 pear in both families, the max- 

 imum venation in C-ecidomyidse 

 is exactly the same as the mini- 

 mum venation in Mycetophilidse. 

 As far as the venation is con- 

 cerned, the two families may be 

 considered as representing de- 

 grees of development along 



exactly the same line, the Mycetophilidse furnishing the transi- 

 tion from the simplest condition, that of the Cecidomyida', to 

 one complex enough to make easy comparison with the mini- 

 mum condition of the Tipulidse. 



The Tipulidffi are a large and quite varied group. The veins 

 are not particularly difficult to homologize, but their homology 



is often disguised by the 

 relative position of the 

 forkings, which results in 

 a series of patterns so 

 different in general ap- 

 pearance that the vena- 

 tion seems at first sight 

 not to be comparable. 

 Fig. 72 shoAvs the varia- 

 tion within the group. 

 The venation of Tipulidte is easily comparable with most of 

 the types of fly venation, and may be considered as represent- 

 ing, if not the primitive, at least the normal venation of Diptera 

 and the most available type for comparison and the determina- 

 tion of homologies. 



The Dexidse constitute a very small family most closely 

 allied to the Tipulida. The venation is given in Fig. 73, but 

 shows nothing particularly significant. 



FIG. 72. Diagram of the venation of Tipu- 

 lidse. Solid lines represent constants, dotted 

 lines variables. Brackets show varying attach- 

 ment at veins. B, indicates concave veins, 

 according to Adolph; R, convex veins: RB, 

 veins considered by that author as concave in 

 some species and convex in others. 



