14 Bulletin 332 



outer, semi-transparent shell are readily distinguished from dor- 

 mant eggs by the decided glossy black appearance of the exposed 

 and unbroken pigmented layer j), ^\hile the portion of the egg 

 covered with the semi-transparent shell has a duller black color. 

 After the outer shell splits and when the young nymph is ready to 

 emerge it exerts pressure along the meso-dorsal line and severs the 

 pigmented layer (plate 1, fig. 7) with the sharp dark-colored ridge 

 or egg burster 6 located along the meso-dorsal line of the head of 

 the nymph. 



The egg burster 6 was observed on the dorsal aspect of the 

 head of A. avemn and A. pami. It coincides with the usual location 

 of the stem of the epicranial suture. During emergence this ridge 

 disappears and only a faint line remains along the meson. No egg 

 burster was seen in the nymphs of A. sorhi, but this was probably 

 due to the fact that the nymphs were not seen immediately after 

 they cut their way through the pigmented layer. The origin and 

 disappearance of the Q^^ burster has not been carefully worked 

 out, but it is possible that this ridge or cutting edge belongs to the 

 exuvium or skin which seems to be shed by the nymph as it emerges. 

 If such is the case this will account for its disappearance. 



The pigmented layer which is severed by the nymph is some- 

 what elastic. This is sho^s^ai in the fact that the Q^g is a trifle 

 larger at the cephalic end after the outer layer splits. Also, the 

 pigmented layer is elevated to a slight extent between the edges of 

 the broken outer layer, as seen in figiires 4, 5 and 6. This elevation 

 is probalily due to the pressure exerted by the nymph within the 

 (igg as it tries to cut its way out. Tlie elasticity is also showTi in 

 hatched eggs, for the pigmented layer contracts somewhat after it 

 is ruptured and the edges of this rupture often coincide with the 

 margin of the broken semi-transparent outer covering (fig. 8 and 

 9). The wriggling and twisting of the nymph as it emerges may 

 also help to push the pigmented layer back to the point where it 

 coincides with the margin of the split outer shell. 



As the nymph of A. avenm starts to emerge it is covered with 

 a thin transparent skin which it sheds before it is out of the shell. 

 This skin is exceedingly thin and very difficult to see. The writer 

 was unable to determine the exact time in the emergence period 

 when the nymphs break this skin. If the egg burster belongs to 

 this first exuvium it is shed a short time before the nymph reaches 

 the stage shown in figure 10. This same membrane in A. pomi 

 apparently is not shed until the nymph is almost out of the shell. 

 Observations concerning the above point need to be repeated for 

 all three species. The nymph of A. avence is usually two-thirds out 

 of the egg before the appendages of the body become free and use- 

 ful. The antennce are the first to be free of the exuvium and the 



