]0 Bulletin 332 



and also as a protection against certain chemicals, it is of little use, 

 as shown in various experiments. 



A third layer, which is a thin transparent membrane, sur- 

 rounds the nymph as it starts to emerge. This layer is shed by the 

 nymph as it emerges, consequently it must be an .exuvium. The 

 cast skin v may be seen as a shriveled white mass at the cephalic end 

 of the opening of a hatched egg. 



The two layers of the egg and the skin about the nymph as it 

 emerges undergo certain changes at the time of hatching, and these 

 are significant, for they have an important bearing upon the re- 

 sponse of the egg to differences in temperature and moisture and 

 to common insecticides and other chemicals. These changes have 

 been observed for two seasons on the eggs of all three species, but 

 they have been observed with special care on the eggs of A. avence. 



In 1917 it was noted that the semi-transparent outer layer 

 t of many eggs of all three species splits (plate 1, fig. 4 and 5) 

 along the meso-dorsal line a short time previous to the emergence 

 of the young nymph. The split starts near the cephalic end (plate 1, 

 fig. 4) and usually extends to the posterior end, and in nine cases 

 out of ten occurs along the meso-dorsal line. In exceptional cases 

 the outer layer t may show several breaks (plate 1, fig. 2 and 3), 

 or the single split may not follow the meso-dorsal line (plate 1, 

 fig. 9). The time interval between the splitting of the outer layer 

 and the rupture of the pigmented layer was not definitely de- 

 termined in 1917, for the significance of the splitting was not 

 realized until it was too late to make the necessary observations. 

 It was observed, however, that the eggs of A. avencB under green- 

 house conditions showed a split outer covering about 48 hours before 

 any hatching occurred, while the eggs of A. pomi under out-of-door 

 conditions showed a split outer shell some eight days before any 

 hatching occurred. During 1918 the first split eggs of A. avence 

 were seen on February 15. Just previous to this date we experi- 

 enced a few warm days after a continuously cold and severe winter. 

 From February 15 on, the percentage of eggs showing a split outer 

 covering increased. The eggs were observed in batches of 200 to 

 500 collected from various orchards. The eggs collected from J. L. 

 Lippincott Company's orchard at Riverton, N. J., showed the 

 following increase in the percentage of eggs with split outer shells 

 (kept out-of-doors) and these observations are typical of eggs 

 collected from other orchards in 1918 : February 19, 2 per cent 

 split; February 26, 10 per cent split; March 1, 20 per cent split; 

 March 4, 25 per cent split; March 11, 33 per cent split; March 19, 

 43 per cent split; and March 25, 47 per cent split (also see dia- 

 gram 1 ) . So far as observed, about 95 per cent of all the live eggs 

 had broken their outer semi-transparent shell before the first 

 njTuphs emerged. 



