BROODS OF 14, 15, OR 16 YEAR PERIODS. as 
The value of a thorough and systematic canvass of the territory 
supposed to be covered by any brood is exhibited in much of the 
work referred to above, and notably in the case of Brood V studied 
by Professors Webster and Hopkins in Ohio and West Virginia. In 
the case of this brood, however, there was no difficulty from an 
association with any 13-year brood. 
Broops or 14, 15, or 16 YEAR Periops. 
The most notable thing about the periodical Cicada is the regularity 
with which it has reappeared during more than 200 years of records 
at the stated intervals of 13 years for the Southern race and 17 years 
for the Northern race. If all the cicadas belonged to a 13-year or a 
17-year period—in other words, if there were but one period—this 
regularity would be less surprising. But the records are so complete 
and full that there can be no doubt whatever of the absolute 
uniformity of periods for the two races for the vast majority of the 
individuals. That unusual conditions will, however, hasten the 
development or retard it a year or more has been already indicated 
on page 24, together with notable examples of artificial acceleration. 
In view of these last instances there can be no doubt that this regu- 
larity of appearance is governed more by the uniformity of tempera- 
ture conditions over a long period of years than from any inherent 
qualities in the insect itself. If these conditions are interfered with, 
however, the Cicada becomes, as it did in the greenhouse at Belvi- 
dere, Ill., accelerated one year; and if such conditions occurred in 
nature over a large area, as already indicated, a new brood would be 
established, but not a 16-year brood, because the climatic conditions 
over the long period of seventeen years, would, and evidently have in 
practically every instance, carried these accelerated or, conversely, 
retarded individuals forward or back to the normal period. There 
are, however, a few records which seem to indicate, and particularly 
in the overlapping territory of the two broods, a variation in the 
length of the subterranean period. These reports of 14-year, 15-year, 
or 16-year broods have been so very scanty that it has not been possi- 
ble to trace them out with any accuracy, but there seems to be no 
reason whatever for doubting the possibility of swarms which have 
actually developed and maintained for a time these intermediate 
periods. In the course of years we may get enough of these records 
to definitely map some of these variant broods. 
31117—No. 71—07——3 
