68 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
district, across the boundaries oi which it may and often docs extend 
its migrations into other regions, but not to become naturalized therein 
We are fully aware that entomologists describe or note specimens, for 
example, of P. migratorius from numerous points immensely distant 
from the boundaries we have assigned it ; but our experience in refer- 
ence to C. spretus has convinced us that unless such specimens are 
known to have been from migrating hordes the evidence is of hut little 
value in determining the question at issue. We freely confess the diffi- 
culty this fact introduces in the attempt to solve the problem ; but when 
we take into consideration the additional fact of the difficulty of dis- 
tinguishing such closely allied species as C. spretus and C. atlantis with- 
out a careful study of their habits, we can find at least one probable 
explanation. 
From the evidence adduced and from our knowledge of our native 
locust, we conclude that each migratory species has its proper native 
habitat or permanent breeding ground, to which, whenever sufficient 
data are obtained, approximate boundaries may be assigned, but that 
as a general rule, to which we know of but one or two exceptions, they 
are essentially migratory within their respective regions of permanent 
distribution. The exceptions alluded to are A. americanum, which is not 
migratory in the United States, but is in the tropical regions, as before 
stated, and P. cinerascens, which is sedentary in parts of Europe at least, 
and also in some other sections. It is possible this is true in reference 
to some other migratory species, but if so we have no evidence of the 
fact ; and, so far as our investigations show, is not true of C. spretus. 
That these permanent areas have expanded in the course of time from 
smaller areas to their present dimensions we think cpaite certain, but we 
will call attention to this hereafter. 
CHARACTER OF THE PERMANENT BREEDING-GROUNDS. 
That locusts prefer comparatively barren regions, or at least sections 
free from arboreal and rank vegetation, has already been affirmed. As 
preliminary to our remarks on this point, we call attention to the fol- 
lowing passage in one of Humboldt's works : 170 
The different quarters of the ■world have been supposed to be characterized by the 
remark that Europe has its heaths, Asia its steppes, Africa its deserts, and America its 
savannas; but by this distinction contrasts are established that are not founded either 
on the nature of things or the genius of languages. The existence of a heath always 
supposes an association of plants of the family Erica ; the steppes of Asia are not 
everywhere covered with saline plants ; the savannas of Venezuela furnish not only 
the graminee, but with them small herbaceous mimosa, legumina, and other dicoty- 
ledonous plants. The plains of Songaria, those which extend between the Don and 
Volga, and the puszta of Hungary are real savannas, pasturages abounding in grasses; 
while the savannas to the east and west of the Rocky Mountains and of New Mexico 
produce Chenopodiums containing carbonate and muriate of soda. Asia has real 
deserts destitute of vegetation in Arabia, Gobi, and in Persia. Since we have be- 
170 Personal Narrative of a Journey to the Equinoctial Regions of the New Continent. Bonn's ed., 
1852, vol. ii, p. 85. 
