INSECTS 



come out the year before or the year after. This fact has 

 suggested the idea that the various broods established at 

 the present time had their origin from individuals of a 

 primary brood that, as we might say, got their dates 

 mixed, and came out a year too soon or a year too late, 

 the multiplying descendants of these individuals thus 

 founding a new brood dated a year in advance or a year 

 behind the emergence time of the parent stock. In this 

 way, it is conceivable, the seventeen-year race might come 

 to appear on each of seventeen consecutive years, and the 

 thirteen-year race on each of thirteen consecutive years. 

 Individuals emerging on the eighteenth or fourteenth year, 

 according to the race, would be reckoned as a part of the 

 first brood of its race. 



The facts known concerning the emergence of the 

 cicadas seem to confirm the above theory, for members of 

 the seventeen-year race appear somewhere every year 

 within the limits of their range, and the emergence of 

 members of the thirteen-year race has been recorded for at 

 least eleven out of the possible thirteen years. All the 

 individuals of a brood are not, of course, descendants of a 

 single group of ancestors, nor do they necessarily occur 

 together in a restricted area — they are simply individuals 

 that coincide in the year of their emergence. However, at 

 least thirteen of the broods of the seventeen-year race are 

 well defined groups, for the most part with definitely circum- 

 scribed territories, though overlapping in many cases. The 

 broods of the thirteen-year race are not so well developed. 



The broods are conveniently designated by Roman 

 numerals. According to the system of brood numbering 

 proposed by Doctor Marlatt, and now generally adopted, 

 the brood of the seventeen-year race that appeared last in 

 1927 is Brood I. This is not a large brood, but it has 

 representatives in Pennsylvania, Maryland, District of 

 Columbia, Virginia, West Virginia, North Carolina, 

 Kentucky, Indiana, Illinois, and eastern Kansas. Brood 

 II, 1928, lives in the Middle Atlantic States, with a few 



I 216 I 



