INSECTS
Immediately after being laid in the fall, the germ nucleus of the aphis egg begins development, and soon forms a band of tissue lying lengthwise on the under surface of the yolk. Then this scarcely-formed embryo undergoes a curious process of revolution in the egg, turning on a crosswise axis head foremost into the yolk and finally stretching out within the latter with the back down and the head toward the original rear end of the egg. Thus it remains through the winter. In March it again becomes active, reverses itself to its first position, and now completes its development.
The date of hatching of the apple aphis eggs depends much upon the weather and will vary, therefore, according to the season, the elevation, and the latitude; but in latitudes from that of Washington north, it is some time in April, usually from the first to the third week of the month. The eggs of most insects resemble seeds in
Fig. 92. Eggs of the green apple aphis with outer coverings split before hatching; below, an egg removed from its covering
their capacity for lying inert until proper conditions of warmth and moisture bring forth the creature biding its time within. The eggs of one of the apple aphids, however, are killed by premature warm weather, or if artificially warmed too long before the normal time of hatching. In general, the final development of the aphis embryos keeps pace with the development of the apple buds, since both are controlled by the same weather conditions, and this coordination usually insures the young aphids against starvation; but the eggs commonly hatch a little in advance of the opening of the buds, and a subsequent spell of cold
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