THE WINGS OF ISOPTERA 135 



(6) THE TRACHEATION AND THE VENATION OF THE WINGS OF THE 



ISOPTERA 



There are two very characteristic features of the venation of the wings 

 of termites, an understanding of which faciHtates the determination of the 

 homologies of the wing- veins : first, the great reduction of the anal area, 

 except in the hind wings of Mastotermes; second, the division of the radius 

 into veins Ri and R^ and the division of the radial sector into veins R2+3 

 and R4+5 in an unusual position, that is very near the base of the wing. 

 This is very clearly shown by the tracheation of the fore wing of Masto- 

 termes described later. 



The typical venation of the wings of the Isoptera and the chief ways in 

 which this type is modified can be well-shown by a study of a series of repre- 

 sentatives of the order consisting of Mastotermes, the most generalized 

 member of the order, Termopsis, a slightly specialized form, and Leiico- 

 ermes one of the more highly specialized forms. 



Comparatively little attention has been given to the study of the 

 tracheation of the wings of members of this order as an aid to the determina- 

 tion of the homologies of the wing-veins. Professor Needham and I 

 secured nymphs of two of the three genera that occur in the United States 

 and photographed the tracheation of their wings; but as this material did 

 not enable us to determine satisfactorily the homologies of the wing-veins, 

 no account of these wings was included in our series of articles. The figures 

 of the tracheation of the wings of Termopsis and of Leucotermes in later 

 paragraphs were made from photographs that we took jointly; and during 

 the preparation of this chapter we have reviewed the subject, having 

 obtained man}^ living nymphs of Termopsis from California and of 

 Leucotermes from Florida. The only published figure of the tracheation of 

 a termite wing is that of Holmgren ('11), who sketches the tracheae in the 

 base of a fore wing of an adult Mastotermes darwiniensis. 



The tracheation and the venation of the wings of Mastotermes dar- 

 winiensis. — Several authors, notable Desneux ('04a and '04b), Silvestri 

 ('09), Holmgren ('11), and Rosen ('13), have published descriptions and 

 figures of the wings of this insect, the most generalized of all living termites 

 known. 



There is no difficulty in recognizing the homologies of the wing-veins 

 excepting those near the costal margin of the wing, i. e. those that lie in 

 front of the media. Here there is considerable difficulty, which is due to the 

 fact that there are variations in the venation and in the tracheation of this 

 part of the wing. Not only do different individuals vary, but the wings of 

 the two sides of the same individual may differ. This is true of the branch- 

 ing of the principal trachea:, which can be seen in the adult wing with com- 

 parative ease, as well as of the venation. 



