DIFFERENCES IN EARLY STAGES OF ALLIED LOCUSTS. 283 



an aspect fresh and bright (Fig. 20, e). If now we examine the cast-off 

 skin, we shall find every part entire with the exception of the rupture 

 which originally took place op the back; and it would puzzle one who 

 had not witnessed the operation to divine how the now stiff hind shanks 

 of the mature insect had been extricated from the bent skeleton left 

 behind. They were in fact drawn over the bent knee-joint, so that 

 during the process they were doubled throughout their length. They 

 were as supple at the time as an oil-soaked string, and for some time 

 after extrication they show the effects of this severe bending by their 

 curved appearance. 



"The molting, from the bursting of the pupa-skin to the full adjust- 

 ment of the wings and straightening of the legs of the perfect insect, 

 occupies less than three-quarters of an hour, and sometimes but half an 

 hour. It takes place most frequently during the warmer part of the 

 morning, and within an hour after the wings are once in position the 

 parts have become sufficiently dry and stiffened to enable the insect to 

 move about with ease; and in another hour, with appetite sharpened by 

 long fast, it joins its voracious comrades and tries its new jaws. The 

 molting period, especially the last, is a very critical one, and during the 

 helplessness that belongs to it the unfortunate locust falls a prey to 

 many enemies which otherwise would not molest it, and not infrequently 

 to the voracity of the more active individuals of its own species." 



DIFFERENCES IN THE IMMATURE STAGES BETWEEN THE ROCKY 



The imaginal differences which characterize these three common and 

 allied species, so often confounded with each other, have been given in 

 Chapter I. In tbis connection, we will indicate those differences which 

 will permit the separation of the three species in the earlier or immature 

 stages. Spretus, though palest when mature, has the most black in the 

 immature stages, and its black face is quite characteristic. One who has 

 great familiarity with these three species in life can distinguish them at 

 any stage (they all three go through the same number of molts), and can 

 even distinguish between the exuviae, those of spretus being darkest, 

 those of atlanis most gray and uniformily speckled, and those of femur- 

 ruhrum palest, with the black streaks more strongly contrasting. 



Spretus. — In the first stage, spretus has a decidedly ferocious look, the head being pro- 

 portionally larger than in the other species. The colors are brown, gray, and dull white, 

 the general tint being light gray, and the insect presenting a mottled and speckled 

 appearance. Of the dark dots and marks, the most conspicuous and presistent (for 

 some specimens are much darker than others) are, one behind the eyes, a subquadrate 

 one on the side of the metathorax, a crescent streak on the sides of the swollen end 

 of the hind femora, and two spots on the bulbous base of the hind tibiae. In the 

 second stage tbe face, with very rare exceptions, is pitchy black, the top of the 

 head showing the three characteristic rows of transverse black marks on a rust- 

 brown ground, the outer rows curving around the eyes, and the middle one broadest, 

 and divided by a narrow medial pale line ; the rust-brown color continues, with more 

 irregular black marks, on the prothorax, narrowing toward its middle ; on each side of 

 it the anterior part of the prothorax is black, relieved below by a conspicuous, arched 

 pale line, and this again with a more or less distinct dark lateral mark beneath. The 



