84 



AN INTRODUCTION TO ENTOMOLOGY 



is often influenced by temperature, being slower in cool nights than 

 in warm ones; and becomiijg slower towards morning if the tem- 

 perature falls. 



In certain genera of crickets as Nemobius and CEcanthus, while 

 each fore wing is furnished with a file and tympana, the scraper of the 

 right wing is poorly formed and evidently not functional. As these 

 insects use only the file of the right wing to set the tympana of the 

 wings in vibration, they may be said to be right-handed. 



Fig- 95- — Wings of a female nymph of CEcanthus (From Comstock and 

 Needham). 



In the Locustidae a similar modification of the function of the 

 stridulating organs has taken place. In all of our common represen- 

 tatives of the family, at least, only one of the files is used. But in 

 these cases it is the file of the left wing that is functional ; we may say, 

 therefore, that so far as observed the Locustidas are left-handed. 

 Different genera exhibit great differences as to the extent of the reduc- 

 tion of the unused parts of the stridulating organs. The file is 

 present in both wings of all of the forms that I have studied ; but the 

 unused file is sometimes in a vestigial condition. The scraper is less 

 persistent, being frequently entirely lacking in one of the wings. In 

 some cases, the tympana of one wing have been lost; but in others 

 the tympana of both wings are well preserved, although only one file 



