70 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
Cossacks and Tartars. It is therefore essentially different from the dis- 
tricts of the two migratory Calopteni, agreeing with them only in want 
of arboreal vegetation and dryness. 
The region which forms the home of A. percgrinum is essentially dif- 
ferent from either of the others. It is composed of the arid and desert 
plains of Northern Africa and Arabia, where rain but seldom falls and 
tropical heat reaches its maximum. Although the term desert has been 
applied to this region, the fact must be borne in mind, as stated by 
Humboldt, that extensive areas in the midst of these deserts are covered 
with at least a scanty vegetation, often sufficient for Hunted pasturage. 
It is therefore apparent that locusts avoid the heavily forest-clad areas- 
and select the open regions as their abode. It is also evident that they 
seek the drier areas, avoiding the moist sections, where the rain precipi- 
tation is abundant. Some, as A. peregrinum and A. americanum,* require 
also the fervent heat of the tropics to develop them in migratory swarms, 
whilst others, as C. spretus, although delighting in the warm sunshine of 
summer days, will, if the atmosphere be dry, flourish in a moderate de- 
gree of cold. 
As heretofore stated, it is much more difficult to draw the line of the per- 
manent distribution of C. spri t its than that which marks the limits of its- 
migrations. That the former falls without (east of) the mountain range 
as far south as Denver, we may assume pretty well settled by the obser- 
vations of the commissioners in person, each having gone over this- 
ground in a different season from the others. That it bends westward 
and enters the mountains a short distance south of this point, we think 
may be safely assumed from the evidence we have obtained. Proceed- 
ing northward from Denver, it bendseastward as we advance, embracing 
the western portion of Nebraska and a large part of Dakota, and extend- 
ing northward from thence into British America, following approximately 
the 103° meridian until it reaches the southern limit of the forests, about 
the 53d parallel of latitude. Thence it bends westward, as given in map 
No. 1. The portion of the plains east of the mountains which should be 
included in this area is a matter of considerable uncertainty, nor is the 
line one that can be rigidly marked. 
The north and northwest boundary appears to be somewhat strictly 
limited by the forest line, though our data in reference to the regions 
beyond this line cannot be considered as conclusive. 
The western boundary is yet a matter of uncertainty, but it is quite- 
probable, from all the facts we have been able to gather, that most of 
Idaho, Wyoming, and the northern half of Utah will have to be included, 
if we define the breeding- grounds in the sense heretofore explained. 
This region may be briefly characterized as follows : Starting at the 
point where the southern boundary of Colorado crosses the 105th me- 
ridian, the main or eastern range of the Eocky Mountains runs almost 
•Note. — Although I have throughout spoken of A. americanum as migratory in Central America, I 
Would not be surprised if the species found migratory there should prore to be distinct. 
