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History of Animals   

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.
The yolk and the white are diverse not only in colour but also
in properties. Thus, the yolk congeals under the influence of cold,
whereas the white instead of congealing is inclined rather to liquefy.
Again, the white stiffens under the influence of fire, whereas the
yolk does not stiffen; but, unless it be burnt through and through, it
remains soft, and in point of fact is inclined to set or to harden
more from the boiling than from the roasting of the egg. The yolk
and the white are separated by a membrane from one another. The
so-called 'hail-stones', or treadles, that are found at the
extremity of the yellow in no way contribute towards generation, as
some erroneously suppose: they are two in number, one below and the
other above. If you take out of the shells a number of yolks and a
number of whites and pour them into a sauce pan and boil them slowly
over a low fire, the yolks will gather into the centre and the
whites will set all around them.
Young hens are the first to lay, and they do so at the beginning
of spring and lay more eggs than the older hens, but the eggs of the
younger hens are comparatively small. As a general rule, if hens get
no brooding they pine and sicken. After copulation hens shiver and
shake themselves, and often kick rubbish about all round them-and
this, by the way, they do sometimes after laying-whereas pigeons trail
their rumps on the ground, and geese dive under the water.
Conception of the true egg and conformation of the wind-egg take place
rapidly with most birds; as for instance with the hen-partridge when
in heat. The fact is that, when she stands to windward and within
scent of the male, she conceives, and becomes useless for decoy
purposes: for, by the way, the partridge appears to have a very
acute sense of smell.
The generation of the egg after copulation and the generation of
the chick from the subsequent hatching of the egg are not brought
about within equal periods for all birds, but differ as to time
according to the size of the parent-birds. The egg of the common hen
after copulation sets and matures in ten days a general rule; the
egg of the pigeon in a somewhat lesser period. Pigeons have the
faculty of holding back the egg at the very moment of parturition;
if a hen pigeon be put about by any one, for instance if it be
disturbed on its nest, or have a feather plucked out, or sustain any

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