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Embyology | |
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Adapted from: Ch. 2 Embryonic Growth and Development Robert E. Ricklefs and J. Matthias Starck, Avian Growth and Development. in Evolution within the altricial precocial spectrum. J. M. Starck and R. E. Ricklefs (eds). Oxford University Press, New York, 1998 http://www.biologie.uni-muenchen.de/ou/morpho/downloads/agd2.pdf
See also: http://embryology.med.unsw.edu.au/OtherEmb/chick1.htm
There is a glossary of terms <here>
Stages of Embryonic Development in Ducks (extrapolated from Chicks)
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<tbody><tr height="5"> <td colspan="4" height="5"></td> <td height="5"></td> </tr> <tr> <td colspan="5" bgcolor="#fff494"> <div align="center"> <font face="Verdana" size="-1"><b>Note: The ages given for the duck embryo assume that development in ducks occurs at the same rate for ducks as it does for chicks.</b></font></div>
</td> </tr> <tr> <td colspan="5" bgcolor="#fff494"> <div align="center"> <font color="#006600" face="Verdana"><b>The First Week</b></font></div> </td> </tr>
<tr> <td bgcolor="#fff494" width="32"></td> <td bgcolor="#fff494" width="100"> <div align="center"> <font face="Verdana" size="-1"><b>Duck</b></font></div> </td> <td bgcolor="#fff494" width="100"> <div align="center">
<font face="Verdana" size="-1"><b>Chicken</b></font></div> </td> <td bgcolor="#fff494"> <div align="center"> <font face="Verdana"><font size="-1"><b>In English</b></font></font></div> </td> <td bgcolor="#fff494"><font face="Verdana"><font size="-1"><b>Scientifically Speaking</b></font></font></td>
</tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <font face="Verdana"><b>0</b></font></div> </td> <td bgcolor="#fff494" width="100"> <div align="center">
<font face="Verdana" size="-1">Just Laid</font></div> </td> <td bgcolor="#fff494" width="100"> <div align="center"> <font face="Verdana" size="-1">Just Laid</font></div> </td> <td bgcolor="#fff494"></td> <td bgcolor="#fff494"></td>
</tr> <tr> <td bgcolor="#ffffcc" width="32"> <div align="center"> <font face="Verdana"><b>1</b></font></div> </td> <td bgcolor="#ffffcc" width="100"></td> <td bgcolor="#faf6ee" width="100"></td>
<td rowspan="2" bgcolor="#ffffcc"><font face="Verdana" size="-1">Preprimitive streak (embryonic shield) 0.3-0.5 mm long</font></td> <td bgcolor="#ffffcc"><font face="Verdana" size="-1">Prestreak stage; two-layered germ disk</font></td> </tr> <tr> <td bgcolor="#ffffcc" width="32"> <div align="center"> <font face="Verdana"><b>2</b></font></div>
</td> <td bgcolor="#ffffcc" width="100"></td> <td bgcolor="#faf6ee" width="100"></td> <td bgcolor="#ffffcc"><font face="Verdana" size="-1">Initial streak</font></td> </tr> <tr> <td bgcolor="#ffffcc" width="32"> <div align="center">
<font face="Verdana"><b>3</b></font></div> </td> <td bgcolor="#ffffcc" width="100"><font face="Verdana" size="-1">15 - 17 hours</font></td> <td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">12 - 13 hours</font></td> <td bgcolor="#ffffcc"><font face="Verdana" size="-1">Intermediate primitive streak</font></td> <td bgcolor="#ffffcc"><font face="Verdana" size="-1">Intermediate streak - extends to about the center of area pellucida.</font></td>
</tr> <tr> <td bgcolor="#ffffcc" width="32"> <div align="center"> <font face="Verdana"><b>4</b></font></div> </td> <td bgcolor="#ffffcc" width="100"><font face="Verdana" size="-1">23 - 24 hours</font></td> <td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">18 - 19 hours</font></td>
<td bgcolor="#ffffcc"><font face="Verdana" size="-1">Definitive primitive streak, ±1.88 mm long<br> Beginning of ailimentary (digestive) tract</font></td> <td bgcolor="#ffffcc"><font face="Verdana" size="-1">Definite streak; </font></td> </tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center">
<font face="Verdana"><b>5</b></font></div> </td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">24 - 29 hours</font></td> <td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">19 - 22 hours</font></td> <td rowspan="5" bgcolor="#fff494" valign="top"><font face="Verdana" size="-1"><b>Day 2:</b></font> <p><font face="Verdana" size="-1">Head process (notochord)<br>
Head fold<br> Start of backbone; nervous system; head; blood islands; eye (primary optic vesicles)<br> ears, heart forming</font></p> </td> <td bgcolor="#fff494"><font face="Verdana" size="-1">Head process; no head folds yet</font></td> </tr> <tr>
<td bgcolor="#fff494" width="32"> <div align="center"> <font face="Verdana"><b>6</b></font></div> </td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">29 - 33 hours</font></td> <td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">23 - 25 hours</font></td> <td bgcolor="#fff494"><font face="Verdana" size="-1">head folds; no somites yet; neural folds appear; vitelline circulation (on the yolk)</font></td>
</tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <font face="Verdana"><b>7</b></font></div> </td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">33 - 34 hours</font></td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">23 - 26 hours</font></td>
<td bgcolor="#fff494"><font face="Verdana" size="-1">one somite</font></td> </tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <font face="Verdana"><b>8</b></font></div> </td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">34 - 38 hours</font></td>
<td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">26 - 29 hours</font></td> <td bgcolor="#fff494"><font face="Verdana" size="-1">4 somites; neural folds meet at level of midbrain</font></td> </tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <font face="Verdana"><b>9</b></font></div>
</td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">38 - 43 hours</font></td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">29 - 33 hours</font></td> <td bgcolor="#fff494"><font face="Verdana" size="-1">7 somites; primary optical vesicles visible; paired primordia of heart begins to fuse</font></td> </tr> <tr> <td bgcolor="#fff494" width="32">
<div align="center"> <font face="Verdana"><b>10</b></font></div> </td> <td bgcolor="#ffffcc" width="100"><font face="Verdana" size="-1">43 - 50 hours</font></td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">33 - 38 hours</font></td> <td rowspan="8" bgcolor="#ffffcc" valign="top"><font face="Verdana" size="-1"><b>Day 3:</b></font> <p><font face="Verdana" size="-1">atrioventricular canal<br>heart starts to beat around here<br><br>Rathke's pouch (it becomes part of the pituitary gland)<br><br>anterior amniotic fold<br>3 primary brain vesicles<br></font></p>
</td> <td bgcolor=“#ffffcc”><font face=“Verdana” size=“-1”>10 somites; cranial flexure begins; 3 primary brain vesicles; heart bent slightly to the right</font></td>
</tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <font face="Verdana"><b>11</b></font></div> </td>
<td bgcolor="#ffffcc" width="100"><font face="Verdana" size="-1">52 - 59 hours</font></td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">40 - 45 hours</font></td> <td bgcolor="#ffffcc"><font face="Verdana" size="-1">13 somites; slight cranial flexure; 5 neuromeres; optic vesicles contrained at base; heart bent to right</font></td> </tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center">
<font face="Verdana"><b>12</b></font></div> </td> <td bgcolor="#ffffcc" width="100"><font face="Verdana" size="-1">58 - 64 hours</font></td> <td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">45 - 49 hours</font></td> <td bgcolor="#ffffcc"><font face="Verdana" size="-1">16 somites; head turning to left; anterior neuropore closed; telencephalon indicated; eyes and stalk well established; auditory pit deep and wide open; heart slightly S-shaped; head fold of amnion covers forebrain</font></td> </tr> <tr>
<td bgcolor="#fff494" width="32"> <div align="center"> <b><font face="Verdana">13</font></b></div> </td> <td bgcolor="#ffffcc" width="100"><font face="Verdana" size="-1">62 - 68 hours</font></td> <td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">48 - 52 hours</font></td> <td bgcolor="#ffffcc"><font face="Verdana" size="-1">19 somites; enlargement of telencephalon; narrowing of auditory pit</font></td>
</tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <b><font face="Verdana">14</font></b></div> </td> <td bgcolor="#ffffcc" width="100"><font face="Verdana" size="-1">65 - 69 hours</font></td> <td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">50 - 53 hours</font></td>
<td bgcolor="#ffffcc"><font face="Verdana" size="-1">22 somites; cranial and trunk flexure well developed; visceral arches 1 & 2; eye begins to grow inward; lens placode is formed; auditory pit opening constricted; Rathke's pouch visisble; amnion extends to somite 7-10</font></td> </tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <b><font face="Verdana">15</font></b></div> </td>
<td bgcolor="#ffffcc" width="100"><font face="Verdana" size="-1">65 - 72 hours</font></td> <td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">50 - 55 hours</font></td> <td bgcolor="#ffffcc"><font face="Verdana" size="-1">Somites 23-25; 3rd visceral arch and cleft visible; optic cup complete.</font></td> </tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center">
<b><font face="Verdana">16</font></b></div> </td> <td bgcolor="#ffffcc" width="100"><font face="Verdana" size="-1">66 - 73 hours</font></td> <td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">51 - 56 hours</font></td> <td bgcolor="#ffffcc"><font face="Verdana" size="-1">Somites26 - 28; primordia of wing and leg present (from mesoderm)</font></td> </tr> <tr>
<td bgcolor="#fff494" width="32"> <div align="center"> <b><font face="Verdana">17</font></b></div> </td> <td bgcolor="#ffffcc" width="100"><font face="Verdana" size="-1">67 - 84 hours</font></td> <td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">52 - 64 hours</font></td> <td bgcolor="#ffffcc"><font face="Verdana" size="-1">Somites 29 - 32; lateral body folds extend around circumference of embryo; tail bud bent under; end of long bone a distinct knob</font></td>
</tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <b><font face="Verdana">18</font></b></div> </td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">84 - 90 hours</font></td> <td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">65 - 69 hours</font></td>
<td rowspan="5" bgcolor="#fff494" valign="top"><font face="Verdana" size="-1"><b>Day 4:<br> </b>start of tongue; continued development of spine; tail; bill; eyes start to get colour<br> premandibular head cavities<br> wing bud; posterior amniotic fold<br> leg bud; epiphysis (end of long bone)<br> </font></td>
<td bgcolor="#fff494"><font face="Verdana" size="-1">somites 30 - 36; leg buds larger than wing buds; trunk fold shifted to lumbal region; tail bud turned right; amnion closed; allantois small</font></td> </tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <b><font face="Verdana">19</font></b></div> </td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">88 - 94 hours</font></td>
<td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">68 - 72 hours</font></td> <td bgcolor="#fff494"><font face="Verdana" size="-1">somites 37 - 40; limb buds symmetrical; trunk flexure dissapeared; tail bud curved, pointing forward; visceral arches: maxillary process distinct swelling, same legth as mandibular process; 2nd visceral arch projects over surface; 4th visceral arch open as a slit</font></td> </tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <b><font face="Verdana">20</font></b></div>
</td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">90 - 94 hours</font></td> <td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">70 - 72 hours</font></td> <td bgcolor="#fff494"><font face="Verdana" size="-1">40 - 43 somites; leg buds assymetrical; rotation of embryo complete; maxillary process same length as or longer than mandibular process; pigmentation of eyes; beginning of retina; 2nd visceral arch projects over surface; 4th visceral cleft open as slit</font></td> </tr> <tr> <td bgcolor="#fff494" width="32">
<div align="center"> <font face="Verdana"><b>21</b></font></div> </td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">4 1/2 days</font></td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">3 1/2 days</font></td> <td bgcolor="#fff494"><font face="Verdana" size="-1">somites 43 - 44; limbs enlarged; wind and leg slightly asymmetrical; maxillary process longer than mandibular process; pigmentation of eyes faint</font></td> </tr>
<tr> <td bgcolor="#fff494" width="32"> <div align="center"> <font face="Verdana"><b>22</b></font></div> </td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">4 1/2 days</font></td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">3 1/2 days</font></td>
<td bgcolor="#fff494"><font face="Verdana" size="-1">somites extend to tip of tail; elongated limb buds; eye pigmentation distinct</font></td> </tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <font face="Verdana"><b>23</b></font></div> </td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">4 1/2 - 5 days</font></td>
<td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">3 1/2 - 4 days</font></td> <td rowspan="3" bgcolor="#fff494" valign="top"><font face="Verdana" size="-1"><b>Day 5:<br> </b>more development of legs, wings, beak<br> Dorsal contour from hindbrain to tail is a curved line<br> </font></td> <td bgcolor="#fff494"><font face="Verdana" size="-1">wing and leg buds about as long as wide</font></td>
</tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <font face="Verdana"><b>24</b></font></div> </td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">5 days</font></td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">4 days</font></td>
<td bgcolor="#fff494"><font face="Verdana" size="-1">toe-plate of legs distinct; 2 humps on mandibular arch; 3 humps on 2nd arch; 4th cleft reduced to small pit</font></td> </tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <font face="Verdana"><b>25</b></font></div> </td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">5 1/2 days</font></td>
<td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">4 1/2 days</font></td> <td bgcolor="#fff494"><font face="Verdana" size="-1">elbow and knee-joints visible; digital plate in wing distinct; 3rd toe; maxilliary process meets nasal groove</font></td> </tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <font face="Verdana"><b>26</b></font></div>
</td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">5 1/2 - 6 1/2 days</font></td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">4 1/2 - 5 days</font></td> <td rowspan="2" bgcolor="#fff494" valign="top"><font face="Verdana" size="-1"><b>Day 6:<br> </b>formation of reproductive organs and differentiation of sex<br> Elbow and knee joints<br>
1st 3 toes<br> </font></td> <td bgcolor="#fff494"><font face="Verdana" size="-1">visceral arches: 2nd forms collar over 3rd & 4th; 3rd 7 4th slit reduced</font></td> </tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center">
<font face="Verdana"><b>27</b></font></div> </td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">6 1/2 days</font></td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">5 days</font></td> <td bgcolor="#fff494"><font face="Verdana" size="-1">grooves between all digits; beak barely visible</font></td> </tr> <tr>
<td bgcolor="#fff494" width="32"> <div align="center"> <font face="Verdana"><b>28</b></font></div> </td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">7 days</font></td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">5 1/2 days</font></td> <td bgcolor="#fff494"><font face="Verdana" size="-1"><b>Day 7:<br>
</b>beak </font><font face="Verdana" size="-1"><br> </font><font face="Verdana" size="-1">3 digits, 4 toes<br> </font></td> <td bgcolor="#fff494"><font face="Verdana" size="-1">2nd & 3rd toe longer than others; neck between "collar" and mandible has lengthened; beak barely visible</font></td> </tr> </tbody></table>
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<table bgcolor="#cc3300" border="0" cellpadding="2" cellspacing="2" width="100%"> <tbody><tr height="5"> <td colspan="5" height="5"></td> </tr> <tr> <td colspan="5" bgcolor="#fff494"> <div align="center"> <font color="#006600" face="Verdana"><b>Weeks 2 - 4</b></font></div>
</td> </tr> <tr> <td bgcolor="#fff494" width="32"></td> <td bgcolor="#fff494" width="130"> <div align="center"> <font face="Verdana" size="-1"><b>Duck</b></font></div> </td>
<td bgcolor="#fff494" width="100"> <div align="center"> <font face="Verdana" size="-1"><b>Chicken</b></font></div> </td> <td bgcolor="#fff494"> <div align="center"> <font face="Verdana"><font size="-1"><b>In English</b></font></font></div> </td>
<td bgcolor="#fff494"><font face="Verdana"><font size="-1"><b>Scientifically Speaking</b></font></font></td> </tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <font face="Verdana"><b>29</b></font></div> </td> <td bgcolor="#fff494" width="130"><font face="Verdana" size="-1">8 days</font></td>
<td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">6 days</font></td> <td bgcolor="#fff494"> <p><font face="Verdana" size="-1">Rudiment of 5th toe<br> </font></p> </td> <td bgcolor="#fff494"><font face="Verdana" size="-1">wing bent in elbow; ear passages visible; can see 5th toe</font></td> </tr>
<tr> <td bgcolor="#fff494" width="32"> <div align="center"> <font face="Verdana"><b>30</b></font></div> </td> <td bgcolor="#fff494" width="130"><font face="Verdana" size="-1">8 1/2 days</font></td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">6 1/2 days</font></td>
<td bgcolor="#fff494"><font face="Verdana" size="-1">legs and wings almost complete (except in size); start of feathers<br> egg tooth<br> </font></td> <td bgcolor="#fff494"><font face="Verdana" size="-1">3 major segments of wing and leg clearly visible; leg bent; feather germs: back; egg tooth distinct</font></td> </tr> <tr> <td bgcolor="#fff494" width="32">
<div align="center"> <font face="Verdana"><b>31</b></font></div> </td> <td bgcolor="#fff494" width="130"><font face="Verdana" size="-1">9 days</font></td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">7 days</font></td> <td bgcolor="#fff494"> <p><font face="Verdana" size="-1">Web between 1st and 2nd digits<br>
</font></p> </td> <td bgcolor="#fff494"><font face="Verdana" size="-1">first movements of eyelids detected; independent limb movements; feather germs: down side</font></td> </tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <font face="Verdana"><b>32</b></font></div>
</td> <td bgcolor="#fff494" width="130"><font face="Verdana" size="-1">9 1/2 days</font></td> <td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">7 1/2 days</font></td> <td bgcolor="#fff494"> <p><font face="Verdana" size="-1">Anterior tip of mandible (lower jaw) has reached beak<br> </font></p> </td>
<td bgcolor="#fff494"><font face="Verdana" size="-1">5th toe gone; wing feathers visible;</font></td> </tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <b><font face="Verdana">33</font></b></div> </td> <td bgcolor="#fff494" width="130"><font face="Verdana" size="-1">9 1/2 - 10 1/2 days</font></td>
<td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">7 1/2 - 8 days</font></td> <td bgcolor="#fff494"> <p><font face="Verdana" size="-1">Web on radial margin of wing and 1st digit<br> </font></p> </td> <td bgcolor="#fff494"><font face="Verdana" size="-1">feather germs: tail</font></td> </tr>
<tr> <td bgcolor="#fff494" width="32"> <div align="center"> <b><font face="Verdana">34</font></b></div> </td> <td bgcolor="#fff494" width="130"><font face="Verdana" size="-1">10 1/2 days</font></td> <td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">8 days</font></td>
<td bgcolor="#fff494"> <p><font face="Verdana" size="-1">Nictitating membrane (third eyelid)<br> </font></p> </td> <td bgcolor="#fff494"><font face="Verdana" size="-1">feather germs: under neck; chest</font></td> </tr> <tr> <td bgcolor="#fff494" width="32">
<div align="center"> <b><font face="Verdana">35</font></b></div> </td> <td bgcolor="#fff494" width="130"><font face="Verdana" size="-1">10 1/2 - 12 days</font></td> <td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">8 - 9 days</font></td> <td bgcolor="#fff494"> <p><font face="Verdana" size="-1">Phalanges (bones & joints) in toes<br>
</font></p> </td> <td bgcolor="#fff494"><font face="Verdana" size="-1">lengthening of beak; feather germs more visible; eyelids start to gorw over eyeball</font></td> </tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <b><font face="Verdana">36</font></b></div>
</td> <td bgcolor="#fff494" width="130"><font face="Verdana" size="-1">13 days</font></td> <td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">10 days</font></td> <td bgcolor="#fff494"><font face="Verdana"><font face="Verdana" size="-1">beak starts to harden</font></font><font face="Verdana" size="-1"><br> </font><font face="Verdana" size="-1">Length of 3rd toe from tip to middle of metatarsal joint = 5.4±0.3mm; length of beak from anterior angle of nostril to tip of bill = 2.5mm; primordium of comb; labial groove; uropygial gland (oil gland at base of tail)<br> </font></td> <td bgcolor="#fff494"><font face="Verdana" size="-1">ends of wings and legs getting longer; (comb in chicks)</font></td>
</tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <b><font face="Verdana">37</font></b></div> </td> <td bgcolor="#ffffcc" width="130"><font face="Verdana" size="-1">14 1/2 days</font></td> <td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">11 days</font></td>
<td bgcolor="#ffffcc"> <p><font face="Verdana" size="-1">Length of 3rd toe = 7.4±0.3mm; length of beak = 3.0 mm<br> </font></p> </td> <td bgcolor="#ffffcc"><font face="Verdana" size="-1">claws - dorsal tips are opaque; plantar pad (under foot) is ridged; feather buds on sternum; eyelids almost close</font></td> </tr> <tr> <td bgcolor="#fff494" width="32">
<div align="center"> <b><font face="Verdana">38</font></b></div> </td> <td bgcolor="#ffffcc" width="130"><font face="Verdana" size="-1">15 - 16 days</font></td> <td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">12 days</font></td> <td bgcolor="#ffffcc"> <p><font face="Verdana" size="-1">Length of 3rd toe = 8.4±0.3 mm; length of beak = 3.1 mm<br>
</font></p> </td> <td bgcolor="#ffffcc"><font face="Verdana" size="-1">scales on legs; external ear almost surrounded by feather germs</font></td> </tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <b><font face="Verdana">39</font></b></div>
</td> <td bgcolor="#ffffcc" width="130"><font face="Verdana" size="-1">17 days</font></td> <td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">13 days</font></td> <td bgcolor="#ffffcc"><font face="Verdana" size="-1">Feathers mostly there.</font><font face="Verdana" size="-1"><br> </font><font face="Verdana" size="-1">Length of 3rd toe = 9.8±0.3 mm; length of beak = 3.5 mm<br> </font></td> <td bgcolor="#ffffcc"><font face="Verdana" size="-1">bill / beak hardening</font></td>
</tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <b><font face="Verdana">40</font></b></div> </td> <td bgcolor="#ffffcc" width="130"><font face="Verdana" size="-1">18 days</font></td> <td bgcolor="#faf6ee" width="100"><font face="Verdana" size="-1">14 days</font></td>
<td bgcolor="#ffffcc"> <p><font face="Verdana" size="-1">Length of beak = 4.0 mm; length of 3rd toe = 12.7±0.5 mm<br> </font></p> </td> <td bgcolor="#ffffcc"><font face="Verdana" size="-1">continued growth and maturation of internal organs</font></td> </tr> <tr> <td bgcolor="#fff494" width="32"></td>
<td bgcolor="#ffffcc" width="130"><font face="Verdana" size="-1">19 - 20 days</font></td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">15 days</font></td> <td bgcolor="#ffffcc"><font face="Verdana"><font face="Verdana" size="-1">beak, claws & scales becoming firm and horny</font></font><font face="Verdana" size="-1"><br> </font><font face="Verdana" size="-1">Length of beak from anterior angle of nostril to tip of upper bill = 4.5 mm; length of 3rd toe = 14.9±0.8 mm<br> </font></td> <td bgcolor="#ffffcc"><font face="Verdana" size="-1">able to hear; sheath begins to cover optic nerves;</font></td>
</tr> <tr> <td bgcolor="#fff494" width="32"></td> <td bgcolor="#ffffcc" width="130"><font face="Verdana" size="-1">21 days</font></td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">16 days</font></td> <td bgcolor="#ffffcc"> <p><font face="Verdana" size="-1">Length of beak = 4.8 mm; length of 3rd toe = 16.7±0.8 mm<br>
</font></p> </td> <td bgcolor="#ffffcc"></td> </tr> <tr> <td bgcolor="#fff494" width="32"></td> <td bgcolor="#fff494" width="130"><font face="Verdana" size="-1">22 days</font></td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">17 days</font></td>
<td bgcolor="#fff494"><font face="Verdana"><font face="Verdana" size="-1">beak turns towards aircell</font></font><font face="Verdana" size="-1"><br> </font><font face="Verdana" size="-1">Length of beak = 5.0 mm; length of 3rd toe = 18.6±0.8 mm<br> </font></td> <td bgcolor="#fff494"></td> </tr> <tr> <td bgcolor="#fff494" width="32"></td> <td bgcolor="#fff494" width="130"><font face="Verdana" size="-1">23 - 24 days</font></td>
<td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">18 days</font></td> <td bgcolor="#fff494"> <p><font face="Verdana" size="-1">Length of beak = 5.7 mm; length of 3rd toe = 20.4±0.8 mm<br> </font></p> </td> <td bgcolor="#fff494"><font face="Verdana" size="-1">eyes open and close; beak claps; starts to tuck</font></td> </tr>
<tr> <td bgcolor="#fff494" width="32"></td> <td bgcolor="#fff494" width="130"><font face="Verdana" size="-1">24 - 25 days</font></td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">19 days</font></td> <td bgcolor="#fff494"><font face="Verdana"><font face="Verdana" size="-1">yolk begins to be pulled into the body cavity</font></font><font face="Verdana" size="-1"><br> </font><font face="Verdana" size="-1">chorio-allantoic membrane (inner membrane lining shell) contains less blood and is "sticky" in living embryo<br> </font></td>
<td bgcolor="#fff494"><font face="Verdana" size="-1">can sleep; vocal apparatus functional</font></td> </tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center"> <font face="Verdana"><b>41</b></font></div> </td> <td bgcolor="#fff494" width="130"><font face="Verdana" size="-1">26 days</font></td>
<td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">20 days</font></td> <td bgcolor="#fff494"><font face="Verdana" size="-1">yolk sac completely drawn into body cavity; embryo occupies almost the entire egg except the aircell; aircell very large</font></td> <td bgcolor="#fff494"><font face="Verdana" size="-1">break into aircell; begins to breathe; makes noise; pips egg; nostrils open</font></td> </tr> <tr> <td bgcolor="#fff494" width="32"> <div align="center">
<font face="Verdana"><b>42</b></font></div> </td> <td bgcolor="#fff494" width="130"><font face="Verdana" size="-1">28 days</font></td> <td bgcolor="#fff494" width="100"><font face="Verdana" size="-1">21 days</font></td> <td bgcolor="#fff494"> <div align="center"> <font face="Verdana"><font face="Verdana" size="-1">HATCH!</font></font></div>
</td> <td bgcolor="#fff494"> <div align="center"> <font face="Verdana"><font size="-1">HATCH</font></font></div> </td> </tr> </tbody></table>
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