68 R. Bigalke 



are first depressed somewhat; then both tonotegmina are raised 

 slightly in the middle line and vibrated rapidly. They move 

 with a see-saw movement in planes transverse to the body. The 

 shrill sound is produced by the inner edge of the right tonotegmen 

 scraping across the teeth on the under surface of the left. This 

 can easily be verified by the following experiment. The observer 

 should carefully approach a stridulating male, from behind if 

 possible, so that he cannot be seen by the insect. Carefully and 

 gently insert the tip of a sharp-pointed instrument under the left 

 tonotegemen and raise it a little. If the insect has not taken 

 fright and stopped the stridulation, it will be noted that though 

 the tonotegmina are still in active vibration no sound can be heard ; 

 immediately the instrument is withdrawn however, the stridulation 

 is plainly audible. While the left tonotegmen is held raised up 

 the whole body of the insect will be seen to quiver violently, show- 

 ing that the muscles which work the tonotegmina must be of con- 

 siderable strength. 



Previously it has been stated that there are about 1 6 chitinous 

 teeth on the ventral surface of the right tonotegmen. Since the 

 left tonotegmen always overlaps the right, it is not clear what 

 function the teeth perform on the right. The fact that the number 

 of teeth on the right tonotegmen is less than the number on the 

 left, and that they do not appear to be as strong as those of the 

 latter suggests that the file on the right tonotegmen is in the 

 process of degeneration. In CrvlUdae both tegmina are provided 

 with a file and a scraper. Thus Landois states that with Cryllus 

 campestris there are from 131 to 1 38 sharp teeth on the under 

 side of one of the veins of each tegmen. The toothed vein of the 

 one tegmen is drawn across a smooth vein projecting from the 

 upper surface of the opposite tegmen. In this species the tegmina 

 may be used indifferently for the purpose of stridulation, i.<r. 

 either the left one drawn across the right, or vice versa. 



In Microcentrum laurifolium, an American locustid, the male 

 has the left tegmen provided with about 55 teeth, and the right 

 tegmen has a scraper at right angles to the file; the sound is pro- 

 duced by the scraper clicking across the teeth as the tegmina are 

 being closed. The tegmina are well veined and serve as 



