110 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
That heat and dryness are the climatic conditions most favorable to 
the development and migrations of the locusts has been maintained by 
all who have paid any particular attention to the subject and have ex- 
pressed their views in reference thereto. Koppen 204 asserts that "Heat 
and dryness are both necessary to the extraordinary increase of the 
locusts;" and the views of other European entomologists accord with 
this. In our former report we expressed the same opinion in reference 
to the development and migrations of the Rocky Mountain locusts. 
Some attempt to show this by the meteorological records was made, and 
although not so full and satisfactory as we desired, was all we were then 
able to present, as there was not time, previous to the date fixed for 
publication, to examine and discuss thoroughly these records in their 
bearing upon this subject, though the material was readily furnished by 
the courtesy of the Chief Signal Officer, to whom we are under many 
obligations for favors on this subject. A further examination of the 
older records and of new data which have been very kindly prepared 
and furnished us by the Signal Service Bureau, a summary of which is 
here presented, has served to somewhat modify our views on this point. 
Not that it has caused us to doubt the general correctness of the state- 
ment that heat and dryness are the climatic conditions most favorable 
to the increase of locusts, and hence of their distribution by migration, 
but that the mode in which these influences operate is not precisely, nor 
so direct and immediate, as heretofore supposed. But before discussing 
the point we will present our additional meteorological data, referring 
the reader to what has been given in our former report in order to avoid 
repeating it here. 
As we shall have occasion to refer repeatedly to Mr. Packard's table 
of locust years, we insert it here as a means of ready reference. 
""Henachr. Siid-Buss, 68. 
