Generation from the egg proceeds in an identical manner with all
birds, but the full periods from conception to birth differ, as has
been said. With the common hen after three days and three nights there
is the first indication of the embryo; with larger birds the
interval being longer, with smaller birds shorter. Meanwhile the
yolk comes into being, rising towards the sharp end, where the
primal element of the egg is situated, and where the egg gets hatched;
and the heart appears, like a speck of blood, in the white of the egg.
This point beats and moves as though endowed with life, and from it
two vein-ducts with blood in them trend in a convoluted course (as the
egg substance goes on growing, towards each of the two circumjacent
integuments); and a membrane carrying bloody fibres now envelops the
yolk, leading off from the vein-ducts. A little afterwards the body is
differentiated, at first very small and white. The head is clearly
distinguished, and in it the eyes, swollen out to a great extent. This
condition of the eyes lat on for a good while, as it is only by
degrees that they diminish in size and collapse. At the outset the
under portion of the body appears insignificant in comparison with the
upper portion. Of the two ducts that lead from the heart, the one
proceeds towards the circumjacent integument, and the other, like a
navel-string, towards the yolk. The life-element of the chick is in
the white of the egg, and the nutriment comes through the navel-string
out of the yolk.

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
other annoyance or disturbance, then even though she had made up her
mind to lay she can keep the egg back in abeyance. A singular
phenomenon is observed in pigeons with regard to pairing: that is,
they kiss one another just when the male is on the point of mounting
the female, and without this preliminary the male would decline to
perform his function. With the older males the preliminary kiss is
only given to begin with, and subsequently sequently he mounts without
previously kissing; with younger males the preliminary is never
omitted. Another singularity in these birds is that the hens tread one
another when a cock is not forthcoming, after kissing one another just
as takes place in the normal pairing. Though they do not impregnate
one another they lay more eggs under these than under ordinary
circumstances; no chicks, however, result therefrom, but all such eggs
are wind-eggs.

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.

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.

Eggs are not symmetrically shaped at both ends: in other
words, one end is comparatively sharp, and the other end is
comparatively blunt; and it is the latter end that protrudes first
at the time of laying. Long and pointed eggs are female; those that
are round, or more rounded at the narrow end, are male. Eggs are
hatched by the incubation of the mother-bird. In some cases, as in
Egypt, they are hatched spontaneously in the ground, by being buried
in dung heaps. A story is told of a toper in Syracuse, how he used
to put eggs into the ground under his rush-mat and to keep on drinking
until he hatched them. Instances have occurred of eggs being deposited
in warm vessels and getting hatched spontaneously.

The sperm of birds, as of animals in general, is white. After
the female has submitted to the male, she draws up the sperm to
underneath her midriff. At first it is little in size and white in
colour; by and by it is red, the colour of blood; as it grows, it
becomes pale and yellow all over. When at length it is getting ripe
for hatching, it is subject to differentiation of substance, and the
yolk gathers together within and the white settles round it on the
outside. When the full time is come, the egg detaches itself and
protrudes, changing from soft to hard with such temporal exactitude
that, whereas it is not hard during the process of protrusion, it
hardens immediately after the process is completed: that is if there
be no concomitant pathological circumstances. Cases have occurred
where substances resembling the egg at a critical point of its
growth-that is, when it is yellow all over, as the yolk is
subsequently-have been found in the cock when cut open, underneath his
midriff, just where the hen has her eggs; and these are entirely
yellow in appearance and of the same size as ordinary eggs. Such
phenomena are regarded as unnatural and portentous.

Birds in general lay their eggs in nests, but such as are
disqualified for flight, as the partridge and the quail, do not lay
them in nests but on the ground, and cover them over with loose
material. The same is the case with the lark and the tetrix. These
birds hatch in sheltered places; but the bird called merops in
Boeotia, alone of all birds, burrows into holes in the ground and
hatches there.

Thrushes, like swallows, build nests of clay, on high trees, and
build them in rows all close together, so that from their continuity
the structure resembles a necklace of nests. Of all birds that hatch
for themselves the hoopoe is the only one that builds no nest
whatever; it gets into the hollow of the trunk of a tree, and lays its
eggs there without making any sort of nest. The circus builds either
under a dwelling-roof or on cliffs. The tetrix, called ourax in
Athens, builds neither on the ground nor on trees, but on low-lying
shrubs.



The egg in the case of all birds alike is hard-shelled, if it be
the produce of copulation and be laid by a healthy hen-for some hens
lay soft eggs. The interior of the egg is of two colours, and the
white part is outside and the yellow part within.

The eggs of birds that frequent rivers and marshes differ from
those of birds that live on dry land; that is to say, the eggs of
waterbirds have comparatively more of the yellow or yolk and less of
the white. Eggs vary in colour according to their kind. Some eggs
are white, as those of the pigeon and of the partridge; others are
yellowish, as the eggs of marsh birds; in some cases the eggs are
mottled, as the eggs of the guinea-fowl and the pheasant; while the
eggs of the kestrel are red, like vermilion.

So much for the generative processes in snakes and insects, and
also in oviparous quadrupeds. Birds without exception lay eggs, but
the pairing season and the times of parturition are not alike for all.
Some birds couple and lay at almost any time in the year, as for
instance the barn-door hen and the pigeon: the former of these
coupling and laying during the entire year, with the exception of
the month before and the month after the winter solstice. Some hens,
even in the high breeds, lay a large quantity of eggs before brooding,
amounting to as many as sixty; and, by the way, the higher breeds
are less prolific than the inferior ones. The Adrian hens are
small-sized, but they lay every day; they are cross-tempered, and
often kill their chickens; they are of all colours. Some
domesticated hens lay twice a day; indeed, instances have been known
where hens, after exhibiting extreme fecundity, have died suddenly.
Hens, then, lay eggs, as has been stated, at all times
indiscriminately; the pigeon, the ring-dove, the turtle-dove, and
the stock-dove lay twice a year, and the pigeon actually lays ten
times a year. The great majority of birds lay during the
spring-time. Some birds are prolific, and prolific in either of two
ways-either by laying often, as the pigeon, or by laying many eggs
at a sitting, as the barn-door hen. All birds of prey, or birds with
crooked talons, are unprolific, except the kestrel: this bird is the
most prolific of birds of prey; as many as four eggs have been
observed in the nest, and occasionally it lays even more.