174 INSECTS INJURIOUS TO VEGETATION. 



which the insects are subject, during the long period of their sub- 

 terranean confinement, is an increase of size, and the more com- 

 plete development of the four small scale-like prominences on 

 their backs, which represent and actually contain their future 

 wings. 



As the time of their transformation approaches, they gradually 

 ascend towards the surface, making in their progress cylindrical 

 passages, oftentimes very circuitous, and seldom exactly perpen- 

 dicular, 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 portion 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 reconnoitre, 

 but descending again on the occurrence of cold or wet weather. 



During their temporary residence in these burrows near the 

 surface, the Cicada grubs, or more properly pupae, for such they 

 are to be considered at this period, though they still retain some- 

 thing of a grub-like form, acquire strength for further efforts by 

 exposure to the light and air, and seem then only to wait for a 

 favorable moment to issue from their subterranean retreats. When 

 at length this arrives, they issue from the ground in great numbers 

 in the night, crawl up the trunks of trees, or upon any other ob- 

 ject in their vicinity to which they can fasten themselves securely 

 by their claws. After having rested awhile they prepare to cast 

 off their skins, which, in the mean time, have become dry and of 

 an amber color. By repeated exertions a longitudinal rent is 

 made in the skin of the back, and through this the included Ci- 

 cada pushes its head and body, and withdraws its wings and limbs 

 from their separate cases, and, crawhng to a httle distance, it 

 leaves its empty pupa-skin, apparently entire, still fastened to the 

 tree. At first the wing-covers and wings are very small and 

 opake, but, being perfectly soft and flejxible, they soon stretch 



