METAMORPHOSES OF THE LOCUST. 279 



ing been kept in a warm room) hatched at the same time. The egg- 

 shells^ bursts open at the head end, when the larva, soon after extricating 

 itself from the egg, casts off a thin pellicle (the amnion, or Faltenblatt)^ as 

 we have se^n in the larvjB of the flea, currant saw-fly, and other insects. 

 Before the skin is cast, the locust is almost motionless, and by slight move- 

 ments of the body in about five minutes draws itself out of the amnion. 

 The process of extrication is as follows : While the larva lies nearly motion- 

 less it puffs out the thin, loose skin connecting the back of the head with 

 the front edge of the prothorax. The distension of this part probably 

 ruptures the skin, which slips over the head, the body meanwhile curving 

 over until the skin is drawn back from the head j when the latter is 

 thrown back, the larva withdraws its antennae and legs, and the skin is in 

 a few seconds pushed back to near the end of the abdomen; finally, its 

 hind tarsi are drawn out of the skin, and in a moment or two more the 

 young locust frees itself and walks actively off, sometimes, however, 

 with the cast skin adhering to the end of the abdomen. 



Before the molting of the amnion, the body and legs are soft and 

 flabby; immediately after, the young locust walks firmly on its legs, and 

 even hops with agility. As we have shown on p. 229, in describing the 

 later stages of the hatching process, the amnion is not shed till the 

 young animal reaches the surface. 



CHAPTER X. 



METAMORPHOSES. 



THE SIX STAGES OF GROWTH. 



We have already seen (p. 237) that the Eocky Mountain locust requires 

 on an average, about seven weeks, from the time of hatching, to attain 



full growth. Belonging to an Order in 

 which the transformations are incomplete, 

 the young locust differs but little in gen- 

 eral structure from its parent. The most 

 striking differences are the want of wings, 

 and the less flattened, narrower prothorax, 

 which rises from the sides more in the 

 riG. 19.-EOCKJ MouNTAix LocusT.-a, shape of a roof. The abdomen is also 



a. newly -hatched larvae ; 6, tall-grown ^ 



larva; c, pupa. (After Riley.) morc roof-shapcd. The perfect winged 



49 Mr. Riley is of the opiuion (see his "Locust Plague in the United States") that in cases where there 

 is requisite heat to insure development, but insufficient moisture to weaken the egg-shell, the terminal 

 spines of the hind tibiae and the tips of the mandibles may assist in rupturing the shell. To use his 

 own words: " Ordinarily all these parts are sheathed in the delicate pellicle {amnio7i). But just in 

 proportion as the hatching is retarded for want of moisture, after the embryon is once fully developed, 

 in that proportion the jaws and spines harden ; and it would seem that by the muscular contractions 

 and expansions of hatching, which bring the ventral parts with great pressure against the shell, there 

 might be slight friction of the horny points which would wear through the delicate amnion and facili- 

 tate the rupture of the shell." He was led to this opinion by having a number of eggs hatch where 

 they had been kept perfectly dry for three months, and by noticing in many cases a transverse rupture 

 at the points in contact with the horny parts mentioned. Ordinarily this action of the spines and 

 jaws does not take place, since the spines at the hatching period are soft, and it cannot be considered 

 as at all proved, even in the exceptional instances stated. 



