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8) 
10 
Descriptions of Embryonic Development 
Day (unincubated): Slightly cloudy area present on 
surface of yolk; blastoderm appearing as white opaque 
spot 2 mm in diameter in center of this cloudy area. 
Day: Blastoderm resembling a bull’s-eye about 10 mm 
in diameter with a small dark central spot surrounded 
alternately by lighter, darker, and lighter circular 
areas. Embryo proper and blood vessels not yet 
visible. 
Days: Tiny blood vessels forming an irregular oval 
8-10 mm in diameter, with unflexed embryo lying 
in clear area in the center; heartbeat not yet visible. 
Days: Embryo, 5-6 mm long, lying transversely to 
longitudinal axis of egg; slightly arched and rotated 
to the right anteriorly. Heartbeat visible. 
Days: C-shaped embryo lying on its left side; eye 
visible as dark pigmented spot 1 mm in diameter. 
Anterior limb buds discernible as small bumps. 
Choroid fissure and heartbeat evident. 
Days: Embryo C-shaped and with prominent eye. 
Choroid fissure, cerebral hemispheres, and midbrain 
obvious; auditory openings barely visible. Limb buds 
appearing as flaplike structures 1 mm long. Allan- 
tois appearing as transparent structure, 34 mm in 
diameter, below lower limb bud. 
Days: Eye about 2 mm in diameter; choroid fissure 
and auditory openings clearly visible. Cerebral hemi- 
spheres and midbrain conspicuous. Anterior limbs 
slightly flexed at elbow joint, posterior limbs covered 
by allantois, which appears as a spherical sac 5-6 mm 
in diameter. 
Days: Embryo still C-shaped, with head nearly as 
large as body. Cerebral hemispheres and bilobed 
midbrain still conspicuous. Eyelids and upper mandi- 
ble beginning to form. Forelimbs terminating in a 
broadened paddle. Long bones of anterior and pos- 
terior limbs visible as opaque white bars. Allantois 
covering entire embryo; heartbeat evident. 
Days: Body and head nearly equal in size. Choroid 
fissure barely visible; iris visible and eyelids well 
formed. Knee and elbow joints flexed. Cerebral hem- 
ispheres less pronounced, but midbrain still promi- 
nent; upper mandible projecting from face. Heart- 
beat still visible. 
Days: Center of each eye encircled by ring of white 
dots, nictitating membrane present. Cerebral hemis- 
pheres and midbrain much reduced; lower mandible 
well defined. First digit of each foot visible and wing 
alulae appearing as thumblike projections. Feather 
germs visible as band of white dots along center of 
back. Heartbeat barely discernible. 
Days: Eyelids beginning to close over eyes. 
separated from manus and patagia formed. Digita- 
tion of feet well advanced. Dark feather papillae 
on back; feather tracts of head appearing as light 
dots. Mandibles assuming normal beak shape; egg 
tooth visible. Heartbeat no longer evident. 
Days: Head more rounded but still large in propor- 
tion to body; choroid fissure no longer visible. Digi- 
tation of feet now complete; toes showing deposition 
of keratin at tips. Dark down feathers appearing 
on back, thigh, and tail. Cloacal opening visible. 
Alulae 
CLOS10 
5M 
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15 
16 
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ESSEX, J. 
HANSON, HAROLD C. 
Days: Feathers on back, thigh, tail, and scapular region 
darkly pigmented; those on back and thigh showing 
color differentiation. Feather germs on eyelids white. 
Keratinization of claws continuing; plantar pads be- 
ginning to form on feet. 
Days: Dark feathers prominent on back, thigh, tail, 
and posterior edge of each wing. Feather germs 
encircling auditory openings dark. Scales beginning 
to form on legs and feet. Nostrils evident and eye- 
lids closing to narrow slits. 
Days: Feathering greatly advanced over that of previ- 
ous stage; dark feathers around auditory opening 
appearing in the form of a semicircle. Inside edges 
of eyelids darkly pigmented. Dark band of feathers 
extending between auditory opening and eye. 
Days: Eyelids virtually closed. Dark feathering around 
auditory opening a complete circle; feathers on breast 
long but colorless. Uropygeal gland showing feathered 
tab above opening. Serrated edge (labial grooves) 
apparent on lower mandible. 
Days: Feathering on head greatly advanced over that 
of previous stage; breast feathers showing dark spots 
at base. Feathers brown on upper eyelids, white on 
lower. Cornified epidermis formed at tips of wing 
alulae. 
Days: Embryo almost entirely covered by down feath- 
ers; uropygeal gland well hidden. Yolk intensely 
yellow in color. Eyelash structures apparent. Toenails 
well developed. 
Days: Size of eyes appearing normal in relation to 
head. Yolk, wrapped around feet and legs of em- 
bryo, with a dark greenish tint. Yolk stalk and audi- 
tory openings plainly visible. 
Days: Scaling of legs nearly complete. Auditory 
openings well hidden by feathers. Yolk being drawn 
into body; stalk no longer visible. Position of embryo 
as follows: lying on left side, with eye, ear, and 
bill visible; right leg bent so that foot is touching top 
of head; right wing in normal position at side. Epi- 
dermal tip on wing alula partly hidden by feathers. 
Days: Embryo in following position: head rotated 
to right, and right wing shifted over head. Elbow 
joint still bare of feathers; periderm still covering egg 
tooth. 
Days: Peridermal covering lost from beak. Back 
arched into pipping position, head covered by right 
wing; air cell punctured by bill, which is projecting 
from under right wing; pipping tooth nearly touch- 
ing shell. Yolk concentrated around feet; embryo 
breathing when removed from egg. 
Days: Upper mandible brownish. Yolk sac reduced 
to sphere 1 mm in diameter. Embyro able to open 
eyes when shell is removed; pipping commencing. 
Days: Pipping completed; embryo emerging as hatched 
quail chick. 
LITERATURE CITED 
R. 1952. Aging techniques applicable to bobwhite 
quail embryos and juveniles. Masters thesis, Ohio State Uni- 
versity, Columbus. 72 p. 
1954. 
lard, wood duck, and bob-white quail eggs. 
267-272. 
Criteria of age of incubated mal- 
Auk 71(3): 
4-65) 
eI 
CEC 14 
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