THE CLASSIFICATION OF THE BROODS. | 27 
three years, there follow seven successive years in which no 13-year 
broods occur. 
Under the supposition that the different broods of the 17-year and 
13-year races sprang in the remote past from an original brood of 
each, it would naturally follow that the broods most closely related 
in time would also present a closer relationship in their range, and 
this, in fact, proves to be generally true. 
To show this relationship and to indicate the natural order of their 
occurrence, I have suggested a new enumeration of the broods in 
which the two races are separated—the 17-year broods coming first, 
followed, for convenience merely, by the i3-year broods. Thus 
Brood XI of the 17-year race becomes Brood I, and the others are 
numbered in the regular order of their occurrence, except that I 
have assigned a brood number to each of the seventeen years. This 
leaves Broods XIJ, XV, and XVII, as newly numbered, without 
any definite colonies, so far accepted, as representatives of established 
broods. As will be shown later, however, there are records which 
indicate the existence of small or scatterme broods filling the three 
gaps mentioned in the 17-year series. 
In renumbering the broods of the 13-year race | have continued 
for convenience from the end of the series of the 17-year race, the first 
13-year brood becoming Brood XVIII, and I have assigned brood 
numbers to each year of the 13-year period, making a total enumera- 
tion of the broods of both races of XXX. As already indicated, six 
of the numbers given to the 13-year race have had no brood assigned 
to them, although records have been secured which seem to indicate 
the existence of scattering broods filling some of the gaps, as will be 
noted in the records given further on. 
It does not necessarily follow, in fact it is quite unlikely, that Brood 
I, as here designated, is the original or oldest brood of the 17-year 
race. Undoubtedly some of the 17-year broods, perhaps half or more 
of them, originated by retardation of individuals, and perhaps half 
by acceleration of individuals; so that the original brood, if it still 
exists, is more’ likely to be one of the intermediate ones. Brood X, 
being the largest of the 17-year broods, perhaps has best claim to 
this distinction. 
For the same reasons an intermediate brood in the 13-year series 
is doubtless the original brood of the 13-year race, and this title may 
possibly belong to Brood XIX, which has the widest range of all the 
broods of the 13-year race. The fewer number of broods in this race 
would seem to indicate that it is of later origin than the 17-year race, 
and this belief is further justified by the fact of its occupying, in the 
main, a territory of later geological formation. 
The following table, beginning with 1893, when the initial broods 
of both the 17-year and the 13-year series appeared in conjunction, 
