152 THE CAUSES WHICH PROPAGATE 



genus Pneumora, who have their musical organs removed from 

 the elytra to the abdomen. In genera o£ Orthoptera, as in 

 butterfliesj the dentieulations of the lima arise from abnormal 

 protrusion or constriction of the helix of the alar trachese or 

 veins ; but in one group they present the appearance of a line of 

 acorn-shaped tubercles. 



The subterranean species of cricket proloug their nympha 

 stage through the winter^s cold^ and many are heard only in 

 spring and summer ; but the bulk of this tribe does not appear 

 till autumn on Pal?earctic areas. Owing to their highly oi'ganised 

 instruments of music, with which they spontaneously express 

 their emotions, the periods of stridulation and repose of the 

 various species are rendered conspicuous. Some Leaf-crickets 

 crepitate hj night ; others are diurnal.- As regards the crickets, 

 many genera are musical by day, but others, as the Mole- 

 crickets, are evening stridulators ; and the House-cricket is 

 nocturnal. The grasshopper tribe is diurnal. 



The conditions which excite specific music may be either 

 observed in the open air or experimented on in the vivarium, when 

 both methods will reveal love and rivalry as its chief phenomena, 

 accompanied with fear proceeding from hearing or sight, but 

 seldom from touch as heretofore. For if we imprison a male, his 

 music, desultory or coming in snatches responsive to artificial 

 tremors from clocks, bells, wheels, horse-hoofs, steam, or to the 

 chirp of birds, is rarely pronounced until another male or his 

 female be introduced, when the sj)ecific notes, with some excep- 

 tion, ring out intense and clear. Thus, if two males be confined, 

 they maintain incessant stridor, and nocturnal kinds prolong 

 their recital through diurnal hours, or vice versa j with the 

 crickets mortal combat invariably concludes this contest. If, on 

 the other hand, the two sexes be enclosed, whenever they ap- 

 proach the male starts into music ; or if a male should bestow a 

 stealthy antennal touch on a female, his rival becomes musical; 

 it is also alleged that female Leaf-crickets, if free, will wing to 

 the stridor of their males. These characters may also be detected 

 in grasshoppers when confined. 



Operating in Nature, such laws tend to band leaf -crickets and 

 grasshoppers in wandering societies, and crickets in associated 

 colonies, due to reiterated masculine challenges and the allure- 



