INSECTA 4^7 



phase. The subsequent decline in numbers leads to the production 

 of solitary non-migrants, i.e. the solitary phase. The two phases 

 differ morphologically, biologically and in distribution so distmctly 

 as to have been regarded as distinct species. Between them are 

 transient individuals which form a series with no fixed characters, 



Fig. 324. Pachytylus migratorius. A grasshopper. Natural size. 

 From Shipley and MacBride. 



merging imperceptibly into the gregarious phase at one end and into 

 the solitary phase at the other. . 



A very characteristic feature of the Saltatoria is the possession ot 

 stridulating organs. In one type, exhibited by the cricket Gryllus, a 

 file on one of the anterior wings is rubbed over a scraper on the other. 



