THE PROCESS OF MOLTING DESCRIBED. 281 



first pupal stage the differences become apparent, and in the true pupa 

 the parts are sufficiently well formed to permit coition, which, as we have 

 had evidence, exceptionally takes place thus prematurely. 



In giving' measurements of the different stages we have taken as 

 near as possible the period of growth between each stage. The depth 

 of coloring varies greatly in the immature stages, and the pale medio- 

 dorsal line, so conspicuous on some of the larvte, is entirely wanting in 

 others. The ground-color after the first stage varies from pale-yellowish- 

 gray, the common and typical color, to orange-brown, and even black, 

 and from pale yellow to pure green. A marked green variety (var. viri- 

 clis Riley) occurs, in which the normal pale yellowish-gray parts are 

 bright green, the green being first distinctly noticeable in the third lar- 

 val stage and enduring to maturity. We have never seen this green 

 variety among the fresh arrivals from the mountain regions, but it is 

 conspicuous among its brown companions when hatching in the Tempo- 

 rary region, and constitutes ordinarily about one in a thousand, though 

 sometimes a much larger proportion, of the progeny of invading swarms. 



THE PROCESS OF MOLTING. 



Like all creatures which suffer exuviation or the shedding of skin, 

 our locust quits feeding for a while and remains quiet during the pro- 

 cess. The first three or larval skins are almost invariably shed on or 

 near the ground, the young insects congregating under grass in little 

 hollows or depressions, or under any shelter that offers for the purpose. 

 The cast-off exuviae are often very abundant in such sheltered places, 

 and are not infrequently mistaken for dead locusts. The last two or 

 pupal molts, on the contrary, more often take place above ground, the 

 insects at these stages of growth preferring to fasten to some elevated 

 object. Immediately after each molt the whole body is soft and color- 

 less, as it was immediately after hatching. 



In order to illustrate the interesting process of molting, we will trace 

 an individual through the last molt — from the pupa to the winged in- 

 sect — as it is the most difficult and, on account of the larger size of 

 the animal, most easily watched. The other molts are very similar in 

 mode of execution. 



" When about to acquire wings the pupa crawls up some post, weed, 

 grass stalk, or other object, and clutches such object securely with the 

 hind feet, which are drawn up under the body. In doing so the favorite 

 position is with the head downward, though this is by no means essen- 

 tial. Eemaining motionless in this position for several hours, with 

 antennae drawn down over the face, and the whole aspect betokening 

 helplessness, the thorax, especially between the wing-pads, is noticed to 

 swell. Presently the skin along this swollen portion splits right along 

 the middle of the head and thorax, starting by a transverse, curved 

 suture between the eyes, and ending at the base of the abdomen. 



