Such as affirm that wind-eggs are the residua of eggs previously
begotten from copulation are mistaken in this assertion, for we have
cases well authenticated where chickens of the common hen and goose
have laid wind-eggs without ever having been subjected to
copulation. Wind-eggs are smaller, less palatable, and more liquid
than true eggs, and are produced in greater numbers. When they are put
under the mother bird, the liquid contents never coagulate, but both
the yellow and the white remain as they were. Wind-eggs are laid by
a number of birds: as for instance by the common hen, the hen
partridge, the hen pigeon, the peahen, the goose, and the vulpanser.
Eggs are hatched under brooding hens more rapidly in summer than in
winter; that is to say, hens hatch in eighteen days in summer, but
occasionally in winter take as many as twenty-five. And by the way for
brooding purposes some birds make better mothers than others. If it
thunders while a hen-bird is brooding, the eggs get addled.
Wind-eggs that are called by some cynosura and uria are produced
chiefly in summer. Wind-eggs are called by some zephyr-eggs, because
at spring-time hen-birds are observed to inhale the breezes; they do
the same if they be stroked in a peculiar way by hand. Wind-eggs can
turn into fertile eggs, and eggs due to previous copulation can change
breed, if before the change of the yellow to the white the hen that
contains wind-eggs, or eggs begotten of copulation be trodden by
another cock-bird. Under these circumstances the wind-eggs turn into
fertile eggs, and the previously impregnated eggs follow the breed
of the impregnator; but if the latter impregnation takes place
during the change of the yellow to the white, then no change in the
egg takes place: the wind-egg does not become a true egg, and the true
egg does not take on the breed of the latter impregnator. If when
the egg-substance is small copulation be intermitted, the previously
existing egg-substance exhibits no increase; but if the hen be again
submitted to the male the increase in size proceeds with rapidity.