SOURCES OF KKKOK IN THK OT.D KKCoRDS. 31 
In tlio case of \\\o l)i-()ods of th(' IT-ycar I'acc. tlic follow in^; cMcikI 
on tlioir southern l)oun(lai-irs into tlic territory of the KJ-yeai- race. 
and lienee the records ol tlie soutliern loeahties ar(> oixmi to >oiiu' 
{(uestion: l^roods \'l, \, XI\ . W'l, 1. 1\', to a sliirlit e\t(Mit also 
in the easi^ oi Broods 11 and 111, and doubtfully in the case of l)idod 
IX, the ])ossil)ility of confusion in this hist l)ro()(l (h'|)en(linL^ on lli(> 
accuracN' i){' \\\v extreme northeastern extension of the l.'l-\-eai' l)roo(l 
XIX. 
Tlie foUowin*: l)roods of the lo-y(»ar rac(> (\xtend noi'thwaid into the 
tcM'ritorv ,occui)i(nl ])\ the 17-N(>ar rac(\ and hence are o|)en to .some 
(luestion: Broods XXIII, XVJll, XIX, and XX. 
The records can not be ((uestioned on this (j^roinul of th(> 17-\('ai" 
Ikoods VIL VTIT, XI, XIII, and V, and of tlie 13-year Broods XX1\ , 
XXI, and XXII, because these ])r()()(ls are limited in distribution 
to the territory of a single race. 
The most notable instance of the overlappintr and conse(|uent piol)- 
abl(^ confusion of the records is seen in the case of Brood X of tlie 
17-year race with Broods XXIII and XIX of the 13-year race. The 
remarkable feature in the distribution of the broods named is the 
notable extension northward in Illinois and Missouri of the 13-year 
Broods XXIII and XIX, which fills almost exactly a district which 
woidd naturally be supposed to belong to the 17-year race and prob- 
ably to Brood X. As pointed out in Bulletin 14, page 26, this circum- 
stance had special significance in view of the fact that the northward 
extension of the 13-year race is based on Broods 'XIX and XXIII, 
and that the records prior to 1898 of the former were collected for the 
most ])art in 1868, when this brood w^as in conjunction with Brood X, 
and of the latter in 1885, when Brood XXIII was also in conjunction 
with Brood X, the limits of which, curiously enough, stop rather 
suddenly at .)r near the eastern State line of Illinois. The possi- 
1)ility \vas immediately suggested that the northern localities assigned 
to Broods XIX and XXIII properly belong to Brood X. 
Tlie occiiiion of the reappearance of the 13-year Brood XXIII in 
is'.is witliout any important 17-year l)rood to confuse tln^ records 
and of the 17-year Brood X in 1902, also without a joint occurrence 
of any important 13-year brood, gave the opportunity wished for to 
determine the validity of old records and to fix more accurately th(> 
distribution of the three broods concerned. 
A Ycry thorough canvass was made in 1S9S of the territory coven^d 
i)y Brood XXIII, and especially the territory in doubt, by calling 
into requisition the very numerous county correspondents of the 
Statistical Division of the Dej^artment of Agriculture and also of the 
^Veather ^Service in adch'tion to tli(> regular correspondents of the 
Division of Entomology. Several thousand replies were received, 
