16 THE PERIODICAL CICADA. 
during which the insect can thrive and increase in size in the southern 
half of its range enables it to go through its development in four 
years less time than in the North, where shorter summers and conse- 
quently shorter periods of growth occur. The chief objections to this 
theory, but not necessarily controverting it, are those made by Drs. 
Smith and Walsh in the quotations given. The problem is, however, a 
very interesting one, and some light may be thrown upon it by the out- 
come of the experiments described under the head following. 
RELATION OF CLIMATE TO THE RACES. 
The anomaly presented of two distinct periods for the completion of 
the adolescent stages of the periodical Cicada, exhibited by the 13-year 
and 17-year races, and its apparent basis in climate led Professor Eiley 
to institute some careful experiments in transferring the eggs of the 
13 year race, collected in various Southern States, to different localities 
in the North, and conversely, eggs of the 17-year race collected in the 
North to localities in the South, to determine the actual influence 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 difference 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 orginally 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. 
The most elaborate experiments in this direction were instituted in 
the summer of 1885 in connection with the joint appearance that year 
of the 13-year Brood VII, which returns this year, and the 17-year 
Brood XXII, which next returns in 190.}. 
In some earlier experiments, made in 1881 with the 13-year Brood 
XVIII, the eggs distributed were in such condition that it was doubt- 
ful whether they ever hatched, and the experiment came to nothing. 
With the later experiments, however, 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. Futhermore, most of the 
transfers were kept under observation for a time to see that the eggs 
actually hatched and the larva? entered the soil in their new situations. 
The record of these transfers is given in detail in the report of the 
Entomologist in the Eeport of the Department of Agriculture for 1885 
(pp. 254-257). So far as the records relate to the experiment of 1885 
this data is rej)roduced in Appendix A. 
