53 



of oue year precedes the next recurrence of Brood XT, with which the 

 series starts: 



Chronological order of the broods of the Cicada from 1893 to 1-910. 



Tear. 



17-year 

 race. 



13-year 

 race. 



Tear. 



17-year 

 race. 



13 -year 

 race. 



]893 



XI 



XII 



XIII 



XIV 



XV 



XVII 



XIX 



XX 



XXI 



XVI 



XVIII 



II 



IV 



VI 

 VII 



1902 



XXII 



I 





1894 



1903 





1895 



1904 





1896 



1905 



V 

 VIII 





1897 



1906 



XVI 



1898 



1907 





XVTTT 



1899 



] 908 



IX 



II 



1900 . . 





1909 . . . 



IV 



1901 



X 



1910 



XI 



VI 









Taking up the 13-year broods in the same way, it will be seen that 

 if the enumeration start with Brood XVI, a 13-year brood follows in 

 regular succession for six years. With the exception of the very doubt- 

 ful Brood X, which is separated from the last 13-year brood by three 

 years, there follows 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 to suggest 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 13-year broods. Thus Brood XI of the 

 17-year race becomes Brood I, and the others are numbered in the reg- 

 ular order of their occurrence, except that I have assigned a brood 

 number to each of the seventeen years. This leaves Broods XII, X Y, 

 and XVII, as newly numbered, without an} 7 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 scattering broods filling the three gaps mentioned in the 17-year 

 series. 



In the renumbering the broods of the 13-year race I 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 num- 

 bers to each year of the 13-year period, making a total enumeration 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 exist- 

 ence 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 



