THE EXTERNAL ANATOMY OF INSECTS 



85 



is used. In these cases it is probable that the tympana of both wings 

 are set in vibration by the action of the single functional file. 



The determination of the homologies of the parts of the wing that 

 enter into the composition of the stridulating organs was accomplished 

 by a study of the tracheation of the wings of nymphs (Comstock and 

 Needham, 'gS-'gp). The results obtained by a study of the wings of 

 CEcanthus will serve as an illustration. 



Figure 95 represents the wings of a female nymph of this genus, 

 with the tracheae lettered. The only parts to which we need to give 

 attention in this discussion are the cubital and anal areas of the fore 

 wing; for it is this part of the wing that is modified in the male to 

 form the musical organ. Both branches of cubitus are present, and 

 Cui bears three accessory branches. The three anal tracheae are 

 present and are quite simple. 



Fig. 96. — Fore wing of a male nymph of CEcanthus (From Comstock and 

 Needham). 



The homologies of the tracheae of the fore wing of a male nymph, 

 Figure 96, were easily determined by a comparison with the tracheae 

 of the female. The most striking difference between the two sexes 

 is a great expanding of the area between the two branches of cubitus 

 in the male, brought about by the bending back of the basal part 

 of Cu2. 



The next step in this study was to compare the wing of an adult 

 male, Figure 97, with that of the nymph of the same sex; and the 

 solution of the problem was soon reached. It can be easily seen that 

 the file is on that part of Cu2 that is bent back toward the inner mar- 

 gin of the wing (Fig. 97, /); the tympana are formed between the 

 branches of cubitus (Fig. 97, t, t); and the scraper is formed at the 

 outer end of the anal area (Fig. 97,5). 



