62 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
tiiie Kepublie is distinct ; nor can we find any reason for believing that 
it is found in South Africa. 
We base our conclusions, therefore, on a careful study of all the evi- 
dence, making the fact of migration an essential requisite. Proceeding 
upon this basis, let us see what conclusion we shall reach in reference to 
the three chief locusts of the eastern continent — P. migratorius, A.pere- 
grinum, and G. italicus. 
To determine what is the permanent home of a migratory species we 
have to rely chiefly upon the following data : 1st. The fact that the 
species has been observed for a series of years inhabiting and reproduc- 
ing itself in a given area, which is the best possible evidence. 2d. Where 
no such data have been obtained, the next best means of determining this 
point is to trace back the lines of migration to the point of departure. 
But in attempting to follow out the latter method caution is necessary 
lest we are led astray by exceptional cases. For illustration, in the great 
invasion of Europe in 1747-'50 it is asserted by the best authority that 
the locusts came from Turkey into Wallachia, Moldavia, Transylvania, and 
Hungary; that in 1749 they passed from thence into Austria and Bava- 
ria, and in 1750 reached Brandenburg. The assumption that Austria 
and Bavaria were native habitats because the brood that proceeded to 
Brandenburg originated there would have been an error, as these locali- 
ties were but stopping places in their western progress. Just as well 
might the people of Nebraska conclude the home of spretus is in the 
south because swarms were observed coming from that direction in 1875 
and 1877, when, in fact, they were the resulting broods of the swarms of 
the preceding years which had passed southward. Kefferstein asserts 
that no existing observations would enable any one to follow any locust 
swarm back from Germany into Tartary, and consequently concluded 
that the hordes originated in the vicinity of the places where they were 
observed. Even those observed in England were believed by him to 
have originated in England. Schrank was also of this opinion. 162 
Yet all the data which Kefferstein presents in reference to the history of 
their migrations in Europe, so far as P. migratorius is concerned, show 
that they proceeded from points eastward of the places visited. 
That there is a large amount of testimony showing that P. migratorius 
is indiginous in a great part of Europe is true. But with the exception 
of one or two witnesses there is a failure to distinguish between this 
species and P. cinerascens. But without stopping to discuss this point, 
which is not essential to the object we have in view, we may add that 
Koppen's own conclusion, shown by the limits of permanent distribution 
he draws, contradicts the larger part of this testimony which relates to 
points north of his line. According to Koppen, great mountain chains 
are powerful obstacles to the diffusion of this species, and that it is rare 
in the southwest of Europe or northwest of Africa where it is almost 
completely replaced by other species, i. e., C. italicus in Spain, Italy, and 
Fauna Boica, Bd. 2, a. i, p. 35. 
