276 Fiftieth Report ox the State Museum 



Seventeen years, less the few weeks spent in the adult and egg states 

 above ground, are passed by this insect in slow growtli and development 

 below the surface. There is but little change, except increase in size, in 

 the appearance of the larva during this long ])eriod, but toward its close 

 there may be noticed four scale-like appendages which represent the 

 rudimentary wings. These ha\-e been gradually developed during the 

 later stages of the larval existence. The emergence of the insect from 

 its underground retreat, although separated by such a long period of 

 years, is remarkably punctual, rarely varying more than a few days from 

 the usual time. In the spring of the seventeenth year the larva makes 

 its way, sometimes with great difficulty from obstacles encountered, to 

 near the surface through a circuitous, smooth, and firmly compacted gal- 

 lery, of a diameter barely sufficient to permit its passage. In its upper 

 portion, at the proper time, it transforms to the pupa, which in turn for.-akes 

 the gallery just before it is ready to assume the perfect form and climbs the 

 nearest tree or other support.* Here the pupa fixes itself firmly and awaits 

 the time for the final change. The pupal shell (PI. IX, fig. 2) soon 

 splits along the back and the creamy-white adult with its red eyes and 

 the black spots on the thorax works itself slowly out of the old case. It 

 is soft just after emerging, and as it dries, the parts begin to harden and 

 slowly to assume the colors natural to the perfect insect. 



The cold weather that prevailed for the first week or two of their 

 appearance, in 1894, resulted fatally to many, and large numbers of the 

 dead might be seen lying upon the ground or cHnging to the trees, — in the 

 latter case often half-way out of the pupal shell. The adults Hve several 

 weeks, feeding at will by means of their beak on the sap of trees. After 

 pairing, oviposition occurs, and the long life-cycle of another brood is 



commenced. 



A Thirteen-Year Brood. 



In the Northern States of the Union this insect occupies seventeen 

 years in completing its round of life as stated above, but in the Southern 

 States, ranging as far north as southern Illinois, there is a form which re- 

 quires but thirteen years for its transformations. It is to all appearances 

 identical with the one occurring in the Northern States, except in a few 

 minor detai's. The greater length of the growing season in the south 

 may perhaps account for the cjuicker development of the larva. Dr. 

 Riley was of the opinion that the thirteen-year for n was but a race of 

 C. septendecim, and not a distinct species. 



* Under certain conditions the larva extends tlie (jallery into an above-ground earthern chamber, 

 which will be noticed hereafter. 



