INSECTS 



wings with the left overlapping the right, and in this position 

 the file of the former lies above the ridge (s) of the latter. 

 I f now the wings are moved sidewise, thejile grating on the 

 ndge or scraper causes a rasping sound, and this is the way 

 the katydid makes the notes of its music. The tone and 

 volume of the sound, however, are probably in large part 

 produced by the vibration of the thin basal membranes of 

 the wings, which are called the tympana (Tm). 



The instruments of different players differ somewhat in 

 the details of their structure. There are variations in the 

 form and size of the file and the scraper on the wings of dif- 

 ferent species, and differences in the veins supporting the 

 tympanal areas, as shown in the drawings of these parts 

 from a conehead (Fig. 27) given at A, B, and C, of Figure 

 19. In the true katydid, the greatest singer of the family, 

 the file, the scraper, the tympana, and the wings them- 

 selves (Fig. 26) are all very highly developed to form an 

 instrument of great efficiency. But, in general, the instru- 

 ments of different species do not differ nearly so much as 

 do the notes produced from them by their owners. An 

 endless number of tunes may be played upon the same 

 riddle. With the insects each musician knows only one 

 tune, or a few simple variations of it, and this he has in- 

 herited from his ancestors along with a knowledge of how 

 to play it on his inherited instrument. The stridulating 

 organs are not functionally developed until maturity, and 

 then the insect forthwith plays his native air. He never 

 disturbs the neighbors with doleful notes while learning. 



Very curiously, none of the katydids nor any member of 

 their family ha; the earlike organs on the sides of the body 

 possessed by the locusts. What are commonly supposed 

 to be their organs of hearing are located in their front legs, 

 as are the similar organs of the crickets. Two vertical 

 slits on the upper parts of the shins, or tibiae (Fig. 19 D, e), 

 open each into a small pocket (Fig. 20 A, E) with a tym- 

 panumlike membrane {Tm) stretched across its inner wall. 

 Between the membranes are air cavities (Tra) and a com- 



[36] 



