200 
IOWA ACADEMY OP SCIENCES. 
In Greene, Guthrie and Adair they may have occurred in the 
valley of the Raccoon or tributaries. 
By river valleys, then, which give really the more impor- 
tant distribution, we can say that they appeared in the Iowa 
valley at Louisa county, were absent or possibly scarce in 
Johnson and Iowa counties, but present in Tama and Marshall 
and north as far as Marshalltown; in the valley of the Skunk 
river from its mouth to Ames in Story county; in the valley of 
the Des Moines and its tributaries as far north as to near Fort 
Bodge and Lehigh, and in the Raccoon in Dallas county; also 
in the valley of the Grand river and its tributaries in Decatur, 
Union and Clairke counties. 
Comparison of the points giving actual occurrence in 1895, 
represented on our map by square black spots, with the out- 
line of Professor Bessey’s map shows a reduction in most of 
the outline, with a slight extension in the Des Moines valley. 
These reports on the whole would suggest a reduction of the 
area, and many of the reports state a reduction in number of 
cicadas as compared with previous occurrences. 
It is of course impossible with the records for even three or 
four occurrences to draw any conclusions as to the future his- 
tory of the insect or assign causes to any apparent changes, 
still seme suggestions as to probable influences may not be out 
of place as indicating lines of future observation and record. 
It is evident that many years must elapse before the problems 
connected with the species can be properly discussed. 
Admitting that the broods in these respective areas have 
declined, it is interesting to inquire into the possible conditions 
affecting the perpetuation of the species. 
It should be borne in mind that the great bulk of settlement 
in these parts of the state occurred between the appearance of 
the broods in 1854-1871 and 1861-1878 respectively, and that 
the settlement resulted in some important changes of the timber 
distribution. These changes took two forms, first a diminution 
of the natural timber belts along the streams from the neces- 
sities for fuel and in much less degree the clearing of limited 
tracts for cultivation. Second, an extension of the timbered 
area by the planting of groves, wind-breaks, orchards, etc., on 
the treeless portions. The former I believe not to have affected 
the area or quantity of timber very greatly, as it would be 
made good by the natural growth and extension and, especially 
as regards the Cicada, had, I believe very little influence. The 
