KUOODS OF 14, ir., OK 1(1 YKAK TKHIODS. 33 
The valiio of a ihoroui^li and sysU'inatic canvass of (lie tci'ritorv 
supposed to be covenul \)\ any brood is exbibited in inncli of the 
work referred to abov{\ and notal)ly in tlie casc^ of Biood \' studied 
])y Professors Webster and Hopkins in Ohio and West XiiMrinia. In 
{ho eas(» of this brood, however, there was no dillicidt y fioni an 
association witli any 13-year brood. 
Ijkoods ok 11, 15, OK H) ^'i;Ait Tiikiods. 
The most notal)h^ thinii: about tlu^ periochcal Cicacbi is tli(M-(\iruhirit v 
with wliich it has reappeared during more than 200 years of rcM-ords 
at th(^ 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 ])eriod — 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 
imiformity of ])eriods for the tw^o 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 vie\N 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 
({ualities in the insect itself. If these conditions are interfered Avith, 
however, the Cicada becomes, as it did in the greenhouse at Belvi- 
dere, 111., accelerated one year; and if such conditions occurred in 
nature over a large area, as already indicated, a new brood w^ould be 
established, but not a 16-year brood, because the climatic conditions 
over the long period of seventeen years w^ould, 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 wdiich seem to indicate, and particularly 
in tin* overlapping territory of the two broods, a variation in the 
length of the subterranean period. These reports of 14-year, 15-year, 
or l()-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 wdiatever 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 
