It is difficult to fix the exact term during which the vitality of an egg remains unextinguished; as it, unquestionably, varies from the very first, according to the vigor of the parents of the inclosed germ, and fades away gradually till the final moment of non-existence. The chickens in stale eggs have not sufficient strength to extricate themselves from the shell; if assisted, the yolk is found to be partially absorbed into the abdomen, or not at all; they are too faint to stand; the muscles of the neck are unable to lift their heads, much less to peck; and although they may sometimes be saved by extreme care, their usual fate is to be trampled to death by the mother, if they do not expire almost as soon as they begin to draw their breath. Thick-shelled eggs, like those of geese, Guinea fowls, etc., will retain life longer than thin-shelled ones, as those of hens and ducks. When choice eggs are expected to be laid, it is more prudent to have the hen which is to sit upon them wait for them, than to keep other eggs waiting for her. A good sitter may be amused for two or three weeks with a few addle-eggs, and so be ready to take charge of those of value immediately upon their arrival. As to the choice of eggs for hatching, such should be taken, of course, as are believed to have been rendered productive. Those of medium size--the average size that the hen lays--are most apt to fulfil this requirement. A very fair judgment may be formed of eggs from their specific gravity; such as do not sink to the bottom in a bowl of tepid water should be rejected. The old-time notion, that small, round eggs produce females, and long, pointed ones males--originally applied, by the ancients, to eating rather than hatching purposes--may be considered exploded. The hen that lays one round egg, continues to lay all her eggs round; and the hen that lays one oblong, lays all oblong. According to this theory, then, one hen would be the perpetual mother of cocks, and another the perpetual producer of pullets; which is absurd, as daily experience proves. The same fate has been meted out to that other venerable test of sex, the position of the air-bag at the blunt end of the shell. "If the vacancy is a little on one side, it will produce a hen; if it is exactly in the centre, a cock." Upon this assumption, the cock should be a very rare bird; since there are very few eggs indeed in which the air bottle is exactly concentric with the axis of the egg. In many breeds, on the contrary, the cockerels bear a proportion of at least one-third, and sometimes two-thirds, especially in those hatched during winter, or in unfavorable seasons; the immediate cause, doubtless, being that the eggs producing a more robust sex possess a stronger vitality.