28 
THE PERTODTCAL CICADA. 
illustrates the new nomenclature su<r<i:;ested, and in parallel columns 
also are given the corresponding nomenclatures proposed Vjy Professor 
Riley, hy Fitch, and the year records in Doctor ^Smith's register: 
Xoimncluhirr of Ou broods of the pcriodkal Ckadu. 
Brood 
3 of the 17-year race. 
Broods of the 13-year race. 
Year. 
Proposed 
enumer- j 
ation. 1 
Rile.v 
num- 
- bers. 
Fitch 
num- 
bers'. 
Smith 
regis- 
ter. 
Proposed 
enumer- 
ation. 
Riley 
nuni- 
bers. 
Fitch 
num- 
bers. 
Smith 
register. 
1893 
I 
II i 
III i 
IV 
^>I 
VII 
VIII 
IX 
X 1 
XI 1 
XII I 
XIII 
XIV 
XV 
XVI 
XVII . 
XI 
XII 
XIII 
XIV 
XV 
XVII 
XIX 
XX 
XXI 
XXII 
I 
i 

5 
7 
2-8' 
4* 
9 
1842 
1843 
1844 
1845 
1846 
1847 
1848 
1849 
1850 
1851 
1852 
1853 
1854 
1855 
XVIII 
XIX 
XX 
XXI 
XXII 
XXIII 
XXIV 
XXV 
XXVI 
XXVII 
XXVIII 
XXIX 
XXX 
XVIII 
XIX 
XX 
XXI 
XVI 
XVIII 
II 
IV 
VI 
VII 
3" 
5' 
1854 
1S94 
1842-1855 
1895 
1843 
189<i 
1844 
1897 
1845 
1898 
184r»-1859 
1899 
1900 . ... 
1901 
X 
1S49 
1902 
1903 
1904 
1905 
V 
VIII 
6 
3 

190G 
XVI 
XVIII 
II 
IV 
3' 
1854 
1907 
1842-1855 
1908 
IX 
1843 
1909 
1844 
The Relationship of the Different Broods. 
As a rule, the relationship of the broods in point of distribution 
agrees ^viih their kinship as indicated by their sequence in time of 
appearance. The relationship indicated by the latter, viz, their 
sequence in time, is doubtless untrustworthy as indicating origin, in 
some instances on account of the uncertainty arising from the action 
of the principle of retardation on the one hand and acceleration on 
the other in the forming of new broods. 
In the case of a ^\ddely scattered brood, like Brood VI, it is quite 
possible that certain swarms originated from a later-appearing brood 
by retardation of individuals, and other swarms from an earlier 
brood by acceleration in time of appearance of individuals.'^ 
This same condition may be true of other of the more scattered 
l:)roods, but with the broods presenting a compact range a singleness 
of origin is evident. 
Examination of the distribution of the broods in connection ^^^th 
their sequence in time of appearance indicates, however, a certain 
" Prof. "\V. E. Castle, ^luseum of Comparative Zoology, Cambridge. Mass., in a letter 
to the writer July 20, 1898, suggested a plausible theory for Brood VI. The isolation 
and wide distribution of this brood leads him to infer that it may be a relatively old 
or ''played out" brood, and if this l)e true it may ho considered the parent of Broods 
Y and VII, the former an offshoot by acceleration and the latter by retardation of 
development. He suggests, however, that the Pennsylvania portion of Brood VII 
may have (u-iginated independently of the New York part, since it lies in the moun- 
tainous country, where the broods would naturally be mixed up more than in any 
other part of the range of the 17-year race. In Ohio he notes that the distinct areas 
