EMBRYO AND EMBRYONIC MEMBRANES 



221 



Rate of Growth of the Allantois. As the embryo lies on its 

 left side, the allantois grows out on the right side of the embryo 

 (Figs. 127 and 130 A) and unites with the chorion about the 

 one hundredth hour. It then spreads rapidly as a flattened sac 

 over the embryo, increasing the extent of the fusion with the 



Fig. 130. — Diagrams showing the relations of the allantois, 

 represented by the tinted area, at different ages. (After 



Hirota.) 

 Alb., Albumen. Alb. S., Edge of albumen-sac.^ All. V., 

 Allantoic vein. am. C, Amniotic cavity. S.-Am., Sero-amm- 

 otic connection. Y. 8., Yolk-sac. . 



A. At 120 hours showing only the amniotic cavity and al- 

 lantois X 2. . • -x ] 1 



B. At 144 hours, showing only the amniotic cavity and al- 

 lantois X 1.2. ^ n^i 1 ii ] 4- 



C. At 192 hours; the entire yolk x .66. Ihe dotted out- 

 line represents the amniotic cavity. , . i. i, ii 



D. At 214 hours. The entire egg after removal ot the shell, 

 X .66. The allximen mass is at the left ; the albumen-sac is be- 

 ginning to form. 



chorion, hence of its outer wall pari passu. At the end of the 

 fifth day it covers more than half of the embryo (Fig. 130 A); 

 at the end of the sixth day the embryo is entirely covered by 



