RELATIONSHIP OF SEVENTEEN-YEAR BROODS. 29 
relationship between the different broods in point of origin, which 
may be indicated as follows: 
THE RELATIONSHIP OF THE SEVENTEEN-YEAR BROODS. 
From the standpoint of distribution the broods of the 17-year race 
may be grouped as follows: (1) Broods I and II; (2) Broods III and 
IV; (8) Brood V; (4) Brood VI; () Broods VII, VIII, IX, X, and 
XI; (6) Broods XII, XIII, XIV, and XV; (7) Broods XVI and 
XVII, the last connecting again with Brood I. 
Taking up these broods in regular order: 
The main body of Brood I occupies territory immediately west of 
the more important and perhaps parent Brood II, and also presents 
a number of colonies extending westward to Kansas. Broods I and 
II seem, therefore, closely allied in point of origin. 
Brood III presents little, if any, relationship to Brood IT in point 
of location and distribution, but is closely allied to the following 
brood, IV, and the latter is evidently a retarded western and southern 
extension of IIT. 
Brood V presents little relationship with Brood IV in point of dis- 
tribution and covers a very compact territory. 
Brood VI, being a widely scattered one, and occurring usually in 
small numbers, does not seem to present any particular relationship 
with any of the preceding or following broods unless the explanation 
suggested by Professor Castle be accepted. 
Brood VII is local in distribution and not very important, and is 
divided into two sections by the territory occupied by the following 
brood, VIII, with which it thus seems to be closely allied. Brood 
IX is very distinctly a southern extension of Broods VII and VIII. 
These three broods seem, therefore, to be closely allied in their 
origin, and, curiously enough, occupy territory which divides the 
two main sections of the great 17-year Brood X, which next follows 
in regular succession, and is perhaps the oldest or parent brood of 
the 17-year race. Brood XI, following X, is evidently an extreme 
northeastern extension of the latter. 
Brood XII is represented by a series of very doubtful records, 
which, if validated in future return periods, will connect the western 
covered by Brood VI lie for the most part just outside the area covered by Brood V 
and on opposite sides of the latter. 
This interpretation by Professor Castle may be in part correct; but in view 
of the wide range of this brood and the very scattering nature and separation of 
the individual swarms, it seems to me more probable to account for it as a develop- 
ment of scattering broods originating for the most part independently by means of 
retardation or acceleration from other broods, and none of the colonies developing 
enough to fill and hold any very large definite territory. In other words, most of the 
colonies are probably of late origin rather than the remnants of an old, extensive, 
worn-out brood, 
