223 THE CAUSES WHICH PROPAGATE 



series of overtures, which they repeat at intervals, raise the 

 abdomen to an ang-le with their thorax, and retain it 

 thus, protruding- and contracting' its segments until exhausted, 

 when they lower it, and the sound simultaneously ceases. 

 The music resulting-, which has duration of from a quarter 

 to half a minute, is a species of trumpeting or whistling ; 

 two or three croaks, and then a continuous dirl resembling- 

 a clock running down, or escape of steam, " Pip ! pip ! 



peee \" I have also noticed one male vibrating 



or beating his closed wings in unison with the notes. The 

 males of T. onii vocalise with no perceptible abdominal motion, 

 and with slight thoracic tremor, and their descant has the 

 colour of stridulation, a metallic or vitreous tone resembling the 

 sound of rubbing rosin on a violin bow, filing of a blacksmith, 

 scraping- of a slate, " Chip ! chip ! chip ! ''■' or mellowed by a 

 sylvan echo, '' Derde ! derde ! derde \" But when commencing 

 this recital, or when alarmed, they deal out their notes without 

 blending them, " Tip ! tip ! tip ! " Their ordinary overtures, 

 with pauses or stresses on a note, are drawn out to twenty 

 minutes, but frequently last only from two to ten, while the 

 harshness of the sounds composing- them is often manifested in 

 the contrast presented by the stridor of a Locusta viridissima 

 from a willow, which then falls on the ear softly as a trickling 

 spring ; plunged beneath water, these sharp notes become a 

 frog-like croak. 



Plebeja as it sings crawls slowly backwards or forwards along 

 the sunny bough. The males incessantly move their abdomens 

 vertically up and down from ten to twenty seconds, a motion that 

 lapses into a tremor ; and these timed series of recitals, a quick 

 rattle like the shaking of coppers, severally shut with a harp-like 

 refrain of five seconds' duration, ^' Whee — whayV'' This note, 

 resembling the breathing of a fly in a spider's toils, and slightly 

 marked also in the pauses of orni, appears due to the aerial 

 vibrations retained, echoed, or prolonged by the drum-covers. 



While the males of Plebeja and Hamatodes in the north of 

 Italy sing" on the summit of brushwood at an elevation vaiying 

 from ten to twelve feet, orni will ascend the poplar trunks to a 

 much greater height; and his notes, as those of Jirematodes, 

 appear capable of being heard at a greater distance than those of 



