LOCUSTS AND GRASSHOPPERS (ACRIDIID^. 115 



the land of their ancestors. Hunger or excessive 

 multiplication, however important as causes of the 

 migration from the Permanent breeding-grounds, seem 

 to have little to do with this return migration, because 

 the insects all depart, whether few or many, and they 

 pass over great stretches of luxuriant vegetation. Pre- 

 vailing winds do not govern them, dangerous obstacles 

 do not stay them. The uncongenial climate of the 

 Temporary region doubtless prompts them to get back 

 to their more congenial native home, and we must 

 allow a certain amount of instinctive guidance akin to 

 that possessed by migratory birds. 



Remarkable Manifestations of Instinct attend Migration. 



The manifestations of instinct that attend migration 

 are indeed remarkable. It is believed that when the 

 locusts migrate, they do so in the direction taken by 

 their predecessors, although several generations may 

 elapse without a migration. Their flight is to a large 

 extent dependent on the wind, and it is said when the 

 air is calm and warm, and they are ready to move, they 

 have the habit of making short flights, circling upward, 

 apparently for the purpose of ascertaining the condition 

 or direction of the upper currents, if they are favourable 

 to bear them away. They support themselves on the 



