RELATION OF CLIMATE TO THE RACES. 19 
of temperature or whether the 13-year race would maintain its normal 
period in the North and the 17-year race in the South. The object of 
the experiment, in other words, was to determine whether the differ- 
ence in time of development between the two races is really one of 
climate and temperature only or whether a fixed characteristic has 
been acquired, not subject to much, if any, modification with changing 
temperature conditions. That the separation was originally caused 
by differences in climate in different parts of the range of the species 
can not be doubted, but the fact that the two races often overlap in the 
adjoining territory of their respective ranges would seem to indicate 
that this time period has become in the course of ages a rather 
permanent feature. 
Doctor Riley’s early experiments in this direction were in 1881 
with the 13-year Brood XIX, but the eggs distributed were in such 
‘condition that it is doubtful if they hatched, and the effort failed. 
A much more elaborate test was instituted in the summer of 1885, 
in connection with the joint appearance that year of the 13-year 
Brood XXIII, which returned in 1898, and the 17-year Brood X, 
which returned in 1902. All possible precautions were observed not 
only to collect the egg-bearing twigs at the right moment and to 
distribute them in fresh, healthy condition, but to see also that they 
were properly placed under suitable trees and that a record was made 
in each instance of the exact locality. Furthermore, most of the 
transfers were kept under observation for a time to see that the eggs 
actually hatched and the larve entered the soil in their new situations. 
The record of these transfers is given in detail in the report of the 
Entomologist, Report of the Department of Agriculture for 1885, 
pages 254-257, and was reproduced in Bulletin 14 as Appendix A. 
The eggs of the 13-year brood were collected in Mississippi between 
July 6 and 17, and distributed to entomologists in New York, Iowa, 
Massachusetts, and Maine in eleven lots. The eggs of the 17-year 
Brood X were collected in Indiana, Pennsylvania, and Michigan, 
chiefly in the latter State, between July 6 and 21, and distributed in 
seventeen different lots to correspondents or entomologists in Georgia, 
Mississippi, Alabama, and Missouri. The preliminary report on the 
condition of this material is given in the appendix cited of Bulletin 14. 
The only positive record received was from Prof. Eugene A. Smith, 
University of Alabama, who found in 1898 one pupal shell and 
noticed several holes in the ground which answered to the description 
of exit openings made by the Cicada. The pupal shell was sent to me 
and proved to belong to the periodical species. That it comes from 
the eggs planted in 1885 seems probable, from the fact that no brood 
was due in this locality in 1898, and this would seem to indicate that 
the 17-year brood may be greatly abbreviated or reduced to the 
13-year term in a warmer latitude. Part of the eggs sent to Professor 
