220 
GENEBAL OBNITHOLOGY. 
duct) wliich conveys the ripened ovum, and in its passage provides it with a quantity of white 
albumen, and finally a chalk shell. A bird's oviduct is the strict morphological homologue 
(p. 68) of a mammal's fallopian tube, uterus and vagina, — 
more accurately, of one fallopian tube, one half of a uterus, 
and one half of a vagina; for the uterus and vagina of a 
mammal result from the union of both miillerian ducts; 
whereas in a bird only one — the left usually — is normally 
developed. Functionally, the oviduct is also analogous (p. 
68) to the mammalian uterus, inasmuch as it transmits the 
product of conception, and detains it for a while, in the initial 
stage of its germination, as we shall see in the sequel ; though 
all but the very first steps in the development of the chick 
are taken during incubation, the egg having so hastily left 
its uterine matrix. These structures — ovary and oviduct, 
fig. 108, — are most conveniently described as we trace the 
course of the ovum from its origination to its maturity. This 
record difiers considerably from the corresponding course of 
events in a mammal, inasmuch as the ovum of a bird, though 
primitively identical with that of any other animal, acquires 
special albuminous and cretaceous envelopes which the mam- 
malian ovum, developed in the body of the parent, does not 
require. The process is termed ovulation. Ovulation, which 
is the formation of an egg in the bird, must not be confounded 
with germination^ which is the formation of a bird in the egg. 
The former can be accomplished by the virgin bird, which 
may lay eggs scarcely differing in appearance from those which 
have been fecundated, but germination in which is of course 
impossible. The course of ovulation, and afterward of germi- 
nation, is now to be traced. 
Fig. 108. — Female organs of do- 
mestic fowl, in activity ; from Owen, 
after Carus. a, 6, c, d, mass of ova- 
rian ova, in all stages of develop- 
ment ; h, a ripe one ; c, its stigma, 
where tlie ovisac or calyx ruptures; 
d, a ruptured empty calyx, to be ab- 
sorbed ; e, infundibulum, or funnel- 
sbaped orifice of the oviduct ; /, next 
portion of oviduct ; g, follicular i)art 
of oviduct ; m, mesometry, membrane 
steadying the oviduct ; the reference- 
line, m, crosses the constricted part or 
isthmus of the oviduct ; these parts 
secrete the white of the egg ; h, shell- 
forming or uterine part of oviduct, 
in which is a completed egg, i; I, 
lowest or vaginal part of oviduct, 
opening into uro-genital sinus of the 
cloaca, 11 ; o, anus. 
vitellus, or yelk, enclosed in a 
Ovulation. — The ovum begins as a microscopic point in 
the ovary, the stroma or tissue of which is packed with these 
incipient eggs. It is primitively just like any other female 
Dynamamceba, from that of a sponge up to that of a woman, 
— a naked simple cell, capable of exhibiting active amoeboid 
movements. It consists of a finely granular protoplasm, the 
delicate structureless cell-w^all, the vitelline membrane, called 
the zona pellucida from its appearance under the microscope. Imbedded in the vitellus is a 
nucleus, or kernel, the germinal vesicle; in this is a nucleolus, or inner kernel, the germinal 
spot The ovum occupies a tiny space in the ovary, the ceUular walls of which constitute an 
ovisac, or graafian follicle. Now if such an ovum as this were mammalian, it would, without 
material change, burst the ovisac, be received into the fallopian tube and conveyed to the 
uterus ; where, supposing it already fertilized, the whole of its contents would develop into the 
body of the embryo. It would therefore be holoblastic (Gr. oXo?, holos, the whole ; ^XaartKos, 
blastikos, germinative). It is difi"erent with a bird or other oviparous " animal, the egg of 
which has to hatch outside the body ; for provision must be made for the nourishment of the 
developing chick, thus separated from the tissues of its mother. Such provision is made by 
the accumulation about the ovum of a great quantity of granular protoplasmic substance, which 
forms nearly all the large yeUow ball called in ordinary language the yelk " of an egg. None 
of this adventitious substance goes to form the embryo ; it is what the embryo feeds on during 
