INSECTS
was at its height, and the eggs are now due to hatch almost any rime. When studying the cicadas of Brood X near Washington in 1919, the writer found the first evidence of hatching on the twenty-fourth of July. Perhaps the normal time of hatching had been delayed somewhat by heavy rains that fell almost continuously during the ten days previous, for many eggs examined during this time were found to be dead and turning brown, though the percentage of these was small. The twenty-fifth was hot and bright all day. The trees were inspected in the afternoon. Their twigs had been bare the day before. Now, at the entrance holes of the egg nests were little heaps of shriveled skins, thousands in all, and each so light that the merest breath of air sufficed to blow it off; so, if according to this evidence thousands of nymphs had hatched and gone, the evidence of as many more must have been carried away by the winds. An examination of many egg nests themselves showed that over half contained nothing but empty shells. Whole series were thus deserted, and usually all or nearly all, of the eggs in any one series of nests would be either hatched or unhatched. But often the eggs of one or more nests would be unhatched or mostly so in a series containing otherwise only empty shells. Delay appeared to go by nests rather than by individual eggs.
As a very general rule the eggs nearest the door of an egg chamber are the ones that hatch first, the others following in succession, though not in absolute order. But unhatched eggs, if present, are always found at the bottom of the nest, with the usual exception of one or two farther forward. Only occasionally an empty shell occurs in the middle of an unhatched row. If the actual hatching of the eggs is observed in an opened nest, several nymphs are usually seen coming out at the same time, and in nearly all cases they are in neighboring eggs, though not always contiguous ones. So this rule of hatching, like most rules, is general but not binding.
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