AGGREGATIONS OF ANIMALS 115 



Many of the sounds made by apparently social 

 animals may be an effect and not a cause at all. 

 They may serve only as a reflex expression of a 

 physiological state given in chorus because many 

 individuals are in the same state of stimulation. 

 Such an interpretation is indicated by watching 

 grasshoppers "singing" on a summer's day. The 

 chorus may be composed of hundreds of voices, 

 yet there is no sign of any moving together or 

 apart as a result of the noise produced. The 

 sounds are made, in this instance, by the grass- 

 hoppers drawing the long hind legs over the horny 

 upper-wing; this fiddling may be kept up for 

 hours on a warm summer's day. Both the adult 

 grasshoppers and the wingless nymphs as well, 

 fiddle away endlessly. Yet the latter have no 

 wings, and are producing no sounds, so that the 

 social significance of the -whole group perform- 

 ance is open to question. 



