ANS 321 Avian Embryo Daily Developmental Changes in the Chick Embryo Day of Incubation "Major" Events 0 -Blastoderm or Blastodisc 1 -Cleavage begins (2) -Embryonic Shield forms -Primitive groove appears -Head folds develop 2 -Primordial heart forms -Blood islands forming -Wolffian ducts differentiate -Optic vesicles form -Cranial flexure begins -Pronephros differentiates then degenerates as mesonephros forms -Head begins to turn to the left -Heart becomes "S" shaped -Amniotic head and tail folds form ( ) = HH Stage 3 -Head fully turned to the left -Allantois begins to form and increase in size -Cranial flexure increased -Yolk stalk forms -Eye pigmentation begins -Amnion surrounds the embryo -A Beating heart is clearly visible -Albumen starts to ‘sink’ to bottom of the egg 4 (21) -Embryo is turned on its left side -Amnion starts contractions -Cranial flexion increases -First active movements of head and neck occur -Chorion and Amnion fuse -Erythropoiesis starts in yolk sac -Proteinase synthesis starts to occur in the yolk sac -Pronephros disappears and metanephros differentiation begins 5 -Definitive RBC synthesis is occurring -Trunk of the embryo starts to move -Bursa of Fabricius begins differentiating -Mesonephros is functioning -Movements of the mouth may be observed 6 (26) -Beak forms -Amnion is beating rhythmically -Limbs are participating in whole body movements -There is active transport of amino acids by the yolk sac (27) 7 -Eye lid and limb movements occur -Egg tooth is now distinctive -Sexual differentiation begins, testosterone production is detectable -The thyroid gland is "concentrating" iodine -Feather formation is detectable in the lumbar-sacral region (29/30) 8 -First movements of eye ball can be detected -Three rows of tail feathers form -Mineralization of bone occurs -Nictitating membrane forms (inner eye lid) -Thyroid is synthesizing mono-iodo-tyrosine (31-32) 9 -Chorioallantoic membrane becomes fixed in relation to the shell Sero-amniotic connection is localized near neck region -Hematopoietic activity in bone marrow occurs -Thyroid now synthesized di-iodo-tyrosine (33-34) 10 -Whole body embryo movements are random and jerky in motion. -Thyroid now secretes thyroxine -Amniotic contractions are reduced -Embryo now positions self at right angle to the long axis of the egg -Legs and body are growing heavier than the head and as a consequence, body is "sinking"into the yolk. (35-36) 11 -Metanephros begins to function (37-38) 12 -Legs are flexed -Albumen absorption occurs through the perforations in the sero-amniotic connections and albumen transfer from albumen sac to yolk via yolk sac umbilicus. Water loss through albumen results in concentrating of albumen proteins. -Mesonephros degenerates -Eye lids cover the eyes -Calcium absorption from the shell commences (39-40) 13 -Head is encased in the yolk sac -Cells of Allantoic endoderm matur -Amnion ceases its contractions -Sero amniotic connection ruptures and albumen transfer (up to 70%) occurs within 24 hours (41-42) -Toe nails and scales are forming 14 -Embryo begins to assume a position along the long axis of the egg. Body turns lengthwise, head follows while neck remains at level of the air -Beak clapping sounds start to be made by the embryo -Auditory sensitivity (response to sound 15 -Stomach begins to contract aidingin the digestion of albumen -Thyroid activity increases -Growth hormone is secreted by adenohypophysis 16 (46) -Embryo growth is continuing -Amino Acid transport system in the duodenum is maturing (47-48) 17 -Embryo begins to lift head from yolk sack to assume "hatch position" -White urate waste material observed in the allantois -air cell size continues to increase -Visual response to light stimuli measured as eye movement (~5% at D 17) (49-50) 18 -Beak of embryo is now "tucked" under the right wing with beak directed towards the air cell (draped position) -Maximum sensitivity to sound increase to 800 Hz -Opens and closes eye lids in response to light 19 (51-52) -Absorption of allantoic fluid is completed -Hatching muscle matures (Musculus complexus) raising the chick’s head -Chick is being forced into the air cell -Yolk sac withdrawal begins 20 -Breathing and vocalization occurs -Prior to breathing, the fluid filling the respiratory system needs to be -Inner shell membrane is pierced by shell tooth, beak is in air cell -Low partial pressure of oxygen Po2 and increased PCo2 > respiratory -As yolk sac is being withdrawn, the yolk sac umbilicus closes off the allantoic circulatory system > forces pulmonary respiration -Yolk sac umbilicus not healed, allantois is drying out (57) -Thyroid hormones function in pipping, etc. (55-56) -Pipping process through shell commences (59, 60, 61) 21 ( ) = HH stages -Chick removes shell cap and "dries-out" (64) -Thermoregulation does not occur until ~ 9 DA and hatching Detailed description of embryonic activities in the egg Kuo, Z. Y., 1931. Ontogeny of embryonic behavior in Aves I. The chronology and general nature of the behavior of the chick embryo. J. Exp. Zool. 61:395-430. 1932. Ontogeny...II. The mechanical factors in the various stages leading to hatching. J. Exp. Zool. 62:453-487.