62 THE PERIODICAL CICADA. 
year 1885, scattered individuals appeared on May 23, and they issued, 
perhaps, most abundantly on the night of the 27th. Those emerging 
within the city were somewhat earlier in appearance than was the case 
in the neighboring woods across the Potomac in Virginia, probably for 
the same reason that the trees in the city put out their foliage a little 
earlier than in the near-by woods. 
Mr. Davis, writing of Brood XII as it appeared in 1894 on Staten 
Island, New York, says that as early as May 19 many Cicadas had 
emerged, the first individuals of the swarm being noted six or seven 
days earlier. 
Mr. A. W. Butler, writing of the brood appearing in 1885 in Frank- 
lin County, Ind., says that while in a few localities individuals were 
seen as early as May 28, in other places not distant they did not 
emerge until June 4, and later. 
Mr. Hopkins made a careful study of the dates of emergence in West 
Virginia in 1897 in connection with Brood XV, and found very consid- 
erable variation in time of appearance both between the northern and 
southern border of the brood and between the lowest and highest ele- 
vations within the area covered by the brood. For the former a differ- 
ence of nearly two weeks was indicated by the records, and for the 
latter a difference of nearly four weeks. This variation, he says, 
appears to be due to the difference of climate between the northern 
and southern sections and between low and high elevations, in the 
former case amounting to 3£ degrees, and in the latter to over 10 
degrees in average summer temperature. He deduces from his obser- 
vations, as a general rule, that there is about three and one-half days 
difference in the time of the first general appearance of the Cicada for 
each degree of difference in the average summer temperature, whether 
it be due to latitude or elevation. 1 
An interesting case of artificial acceleration in the appearance of 
these insects is recorded by Professor Eiley as follows: Dr. E. S. Hull, 
of Alton, 111., having placed some underground Hues for forcing vege- 
tables, the unnatural heat caused the Cicadas to emerge by the 20th of 
March and from this time on until May. Other instances of accel- 
eration are given in the discussion of the subject of retardation or 
acceleration in times of appearance as a possible explanation of the 
formation of the different broods. (See p. 20.) 
Notwithstanding the difference in time of emergence in the above 
citations, the fact nevertheless remains true of the great uniformity 
evidenced in the time of emergence, namely, the last week in May, for 
the great bulk of the territory covered by the different broods of the 
Cicada, and this fact is one of the noteworthy features in the life his- 
tory of the insect. 
The males precede the females by several days and disappear earlier 
in the summer, both by reasou of being shorter lived and also on account 
Bulletin 50, W. Va. Agric. Exper. Station, p. 17. 
