RELATIONSHIP OF THE DIFFERENT BROODS. 27 
the northern localities assigned to Brood XVIII and VII in Illinois 
and Missouri properly belong to Brood XXII. 
The problem will be better understood if the maps depicting the 
individual territory of the broods concerned be examined. The records 
of Brood XXII of 1885, which might have settled the question, were, as 
noted, again rendered somewhat uncertain on account of the joint 
occurrence that year of Brood VII, although in general they seem to 
have confirmed the previous records. At any rate, there is still sufficient 
question as to the accuracy of the distribution of the several broods 
mentioned to warrant the taking of considerable pains to secure accurate 
and full records of their distribution on the occasions of their next 
recurrence. Of Brood VII, it is hoped that the true range will be 
determined the present year. 
Many of the other scattering records of 13-year broods northward 
of the general range of the 13-year race, and similarly of the 17-year 
broods southward, may possibly be based on small and unimportant 
swarms of either race which have not been defined as regular broods, 
and occurring in conjunction with the known 17-year or 13-year broods 
have been erroneously assigned to one or other of these broods. 
The range also of the individual broods is undoubtedly much greater 
than the limits now assigned, since the records are largely based on the 
notable and dense swarms, and rarely take into account the scattering 
individuals which undoubtedly extend over a much greater territory 
and usually pass unnoticed. An illustration of this is given the present 
season by the finding of a few individuals here and there in the District 
of Columbia and in adjacent territory in Virginia, probably referable 
to Brood XVII, although this brood has never before been recorded 
as occurring here. 
THE RELATIONSHIP OF THE DIFFERENT BROODS. 
A study of the maps of the several broods emphasizes what has been 
elsewhere suggested on the subject of their relationship in point of 
origin. It can not be questioned but that the time of appearance is 
a more important consideration in determining relationship than is the 
distribution, and in fact the broods have been classitied, as already 
seen, solely on the ground of time of appearance. 
Considering first the broods of the 13-year race, it will be noted that 
if we begin our enumeration with Brood XVI a 13-year brood follows 
each year consecutively for six years. With the exception of the very 
doubtful and unimportant Brood X, which is separated from the last 
13-year brood by three years, there follow seven successive years in 
which no 13-year brood appears. (See table, p. 23.) 
The relationship of the 13-year broods seems to be as follows: 
Brood XVI is a rather insignificant one, and, as wo have elsewhere 
stated, is undoubtedly an eastern extension or offshoot of the great 
13-year Brood XVIII, which succeeds it. Brood 11 is undoubtedly a 
