In this article we will about the dissection and structure of chick embryo.
Dissection of Chick Embryo:
Break the egg shell at the narrow end by striking it gently with the handle of a scalpel. Remove the egg shell in pieces with a pair of forceps till the opening is large enough to pour out the contents without damaging the vitelline membrane around the yolk.
Pour the contents of the egg in a clean petri dish. In the animal pole the embryo appears as a small white body on the surface of the yolk at the centre. Hold the vitelline membrane with a pair of fine forceps and cut it close to the embryo with a pair of fine, sharp scissors.
Separate the embryo from the underlying yolk and transfer it to a watch glass containing physiological solution. Wash out the yolk with a fine brush. Stain the embryo with borax carmine in a watch glass. Wash, dehydrate, clear and mount in Canada balsam or DPX.
Different Structure of a Chick Embryo:
Structure of an 18 Hours Chick Embryo:
(Fig. 32.1)
1. Area opaca and area pellucida quite distinct.
2. Primitive streak, a longitudinal, median thickening.
3. Neural groove, neural folds, sub- cephalic pocket, proamnion and head fold differentiated.
Structure of a 24 Hours Chick Embryo:
(Fig. 32.2)
1. Area vasculosa and area pellucida distinct.
2. Primitive streak in a reduced state.
3. Neural folds well developed towards the anterior end.
4. Primary optic vesicles in an early stage of development.
5. Foregut differentiation discernible.
6. Paired heart rudiments with dorsal and ventral aortae present.
7. Somites four pairs in the middle of the body.
Structure of a 33 Hours Chick Embryo:
(Fig. 32.3)
1. Primitive streak restricted to posterior end.
2. Head bent ventrally.
3. Neural folds fused in the brain region except the neuropore.
4. Three primary brain vesicles, prosencephalon, mesencephalon and rhombencephalon differentiated.
5. Notochord distinct.
6. Foregut elongated.
7. Heart rudiment tubular and bent to the right.
8. Somites 12 pairs.
Structure of a 48 Hours Chick Embryo:
(Fig. 32.4)
1. Primitive streak greatly reduced.
2. Amnion in a very early stage.
3. Both cranial and cervical flexure developed.
4. Neural tube differentiated into brain and spinal cord.
5. Optic cups prominent.
6. Auditory vesicles distinct.
7. Three pairs of arterial arches arise from the ventral aorta.
8. Somites 26 pairs.
Structure of a 72 Hours Chick Embryo:
(Fig. 32.5)
1. The cranial flexure is maximum.
2. Appendage rudiments present.
3. Optic cups with distinct, closed retina and lenses.
4. Auditory vesicles connected to the ectodermal aperture through ductus endolymphaticus.
5. Head fold grows back and lies between 10 to 18 somites.
6. Pharynx and four pharyngeal pouches formed.
7. Somites 35 pairs.