PERIODICAL CICADA. 129 



60 far under ground in the active period of the year. The latter must 

 be supposed to have been the case, in the present instance, the insects 

 having been found as early as the fifth of September. Such facts, taken 

 in connection with the circumstance that vegetation does not usually 

 appear to suffer from their subterranean feeding, go to show that their 

 usual range is several feet below the surface. But this only leaves the 

 nature of their food involved in the greater uncertainty. 



Such accounts as these are very unsatisfactory, but they may serve 

 to draw attention to those parts of the Cicada's history which most 

 stand in need of elucidation. 



TIME OF APPEARANCE AND DISAPPEARANCE. 



A period of from five to six weeks covers the whole time in which 

 the Cicadas are seen in their perfect or winged state. At the time of 

 the appearance of the toore southern brood in 1868, Mr. Riley states 

 that he saw the first Cicada on the 22d of May, and that none were to 

 be seen after the fourth of July. My observation of the northern brood 

 coincides almost precisely with this — having seen the first on May iiSd, 

 and the last on the Ist of July. Mr. Wier wrote to me that he first 

 saw them on southern exposures, at Lacou, on the 19th of May. Dr. 

 Smith states, that in Maryland and Pennsylvania, their time of emer- 

 gence from the ground was from the 20th to the 25th of May, thus cor- 

 responding precisely with the periods recorded above, and showing a 

 remarkable uniformity in the time of their appearance in difi'erent lati- 

 tudes, and remote localities. Straggling individuals, however, continue 

 to emerge long after their general appearance. I saw instances of this 

 as late as the 12th and the 17th of June. 



GEOGRAPHICAL EXTENT OF THE BROOD OF 1871. 



. A good deal of interest has heretofore been taken by others as well 

 as entomologists, in tracing the geographical outlines of the different 

 broods of the so-called 17-year locust. It seemed, therefore, to be one 

 of the special duties of the State Entomologist of Illinois, in the season 

 of 1871, to determine, as nearly as possible, the range of the present 

 brood, and to make a record of it, which may be consulted by those who 

 may take an interest in this matter, seventeen years hence. I have, 

 therefore, entered into a somewhat extensive correspondence upon this 

 subject, with persons in different parts of this and the neighboring 

 States. The following is a condensed statement of the results of these 

 inquiries : 



