EXPLANATION TO PLATE I. 



Country in which the species is not indigenous ; 

 which it visits at irregular intervals ; in which it 

 is most disastrous ; and which it vacates within a year. 



Area more often visited ; in which the species holds 

 its own longer, but which it generally forsakes in the 

 course of time. 



Region where the species comes to perfection ; in 

 which it permanently breeds ; and from which come 



the disastrous swarms that sweep over the first mentioned 



region. 



Area west of the mountains where the species also, 

 in all probability, breeds permanently ; from, which 



it sometimes pushes to the east of the mountain range ; 



and from which the California swarms probably come. 



