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 Mirshalltown; 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 

 Dodge and Lohigh, and in the Raccoon in Dallas county; also 

 in the valley of the Grand river and iis tributaries in Decatur, 

 Union and Clarke 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 futare his- 

 tory of the insect or assign causes to any apparent changes, 

 still some suggestions as to probable inflaences 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 IS'dI-ISTS 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 streancs 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 inflaence. The 



