EMBRYO AND EMBRYONIC MEMBRANES 221 



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

 ieft 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 



d.r^'.^. 



<^m.C. 



J//.P^.A 



'■'J.-A72. 





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 vem. am. C, Amniotic cavity. S.-Am., Sero-amni- 

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

 1 t"^* ^^o^^ ^ouTs showing only the amniotic cavity and al- 



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

 lantois X 1.2. 



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

 line represents the amniotic cavity. 



A?" '^V^^^,?^^'^®- ^^^ ^"^^^^ ^g^ ^fter removal of the shell, 

 X .bb. 1 he albumen 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 



