INSECTS 



cases by the splitting of an outer sheath of the egg (Fig. 

 92), exposing the glistening, black, true shell of the egg 

 within. Then, from one to several days later, the shell 

 itself shows a cleft within the rupture of the outer coat, 

 extending along half the length of the exposed egg sur- 

 face and down around the forward end (Fig. 93 C). 

 From this split emerges the soft head of the young aphis 

 (D), bearing a hard, toothed crest, evidently the instru- 

 ment by which the leathery shell was broken open, and 

 for this reason known as the "egg burster." Once ex- 

 posed, the head continues to swell out farther and far- 

 ther as if the creature had been compressed within the 

 egg. Soon the shoulders appear, and now the young 

 aphis begins squirming, bending, inflating its fore parts 

 and contracting its rear parts, until it works its body 

 mostly out of the egg (E, F) and stands finally upright 

 on the tip of its abdomen which is still held in the cleft 

 of the shell (G). 



The young aphis at this stage, however, like the young 

 roach, is still inclosed in a thin, tight-fitting, membranous 

 bag having no pouches for the legs or other members, 

 which are all cramped within it. The closely swathed head 

 swells and contracts, especially the facial part, and sud- 

 denly the top of the bag splits close to the right side of 

 the egg burster (Fig. 93 H). The cleft pulls down over 

 the head, enlarges to a circle, slides along over the shoul- 

 ders, and then slips down the body. As the tightly stretched 

 membrane rapidly contracts, the appendages are freed 

 and spring out from the body (I). The shrunken pellicle 

 is reduced at last to a small goblet supporting the aphid 

 upright on its stalk, still held by the tip of the abdomen 

 and the hind feet (I). To liberate itself entirely the 

 insect must make a few more exertions (J), when, finally, 

 it pulls its legs and body from the grip of the drying 

 skin, and is at last a free young aphid (L). 



The emergence from the egg and from the hatching 

 membrane is a critical period in the life of an aphid. The 



f 160 1 



