204 



MIGRATION 



states that swarms starting in a given direction are not readily turned 

 back. For many years previous to 1932, it was believed that there 

 would be no more outbreaks accompanied by migration. Migration 

 reappeared, however (1932, etc.), but not in the spretiis phase, and 

 again the states immediately west of the Mississippi were visited. 



Longitude 



Fig. 46. — Showing the permanent breeding area and the outward migration of 

 the grasshopper (Melanoplus mexicanus spretus) in 1876. (After Packard and 



Thomas, 1878.) 



Return migration or remigration is well illustrated for mexicanus, the 

 outward flight in Fig. 46 (1876) (Packard and Thomas, 1878), and the 

 extensive return flight in Fig. 47 (1877). The location of the egg- 

 depositing area is also shown. The phenomena of migration in grass- 

 hoppers, while perhaps more fully explained than those of birds, are 

 hardly less remarkable (cf. Packard, 1880). 



