THE SEVENTEEN-YEAR CICADA. 
215 
and about an inch in diameter, she gathered twenty-three 
larvae ; they were of various sizes, from a quarter of an inch 
to an inch in length. They were on all the roots that grew 
deeper than six inches below the surface. The roots were 
unhealthy, and bore the appearance of external injury from 
small punctures. On removing the outer coat of bark, this 
appearance increased, leaving no doubt as to the cause of the 
disease.” * 
The grubs do not appear ordinarily to descend very deeply 
into the ground, but remain where roots are most abundant ; 
and it is probable that the accounts of their having been dis- 
covered ten or twelve feet from the top of the ground have 
been founded on some mistake, or the occurrence of the 
insects at such a depth may have been the result of accident. 
The only alteration to which the insects are subject, during 
the long period of their subterranean confinement, is an 
increase of size, and tbe more complete development of the 
four small scale-like prominences on their backs, which rep- 
resent and actually contain their future wings. 
As the time of their transformation approaches, they grad- 
ually ascend towards the surface, making in their progress 
cylindrical passages, oftentimes very circuitous, and seldom 
exactly perpendicular, the sides of which, according to Dr. 
Potter, are firmly cemented and varnished so as to be water- 
proof. These burrows are about five eighths of an inch in 
diameter, are filled below with earthy matter removed by the 
insect in its progress, and can be traced by the color and 
compactness of their contents to the depth of from one to two 
feet, according to the nature of the soil ; but the upper por- 
tion to the extent of six or eight inches is empty, and serves 
as a habitation for the insect till the period for its exit arrives. 
Here it remains during several days, ascending to the top of 
the hole in fine weather for the benefit of the warmth and 
the air, and occasionally peeping forth, apparently to recoil- 
* Proceedings of the Academy of Natural Sciences, Philadelphia, Nov. and 
Dec., 1840 ; and Downing’s Horticulturist, Vol. II. p. 10, July, 1847. 
