From Sixth Day to Hatching 281 



very marked. The structures around the 

 mouth have assumed more avian outlines ; 

 while in the floor of the mouth the tongue 

 has begun to develop, as a bud of mesoblast 

 covered with ectoblast. 



The eighth, ninth, and tenth days. — About 

 the only change noticed in the amnion is a 

 diminution in the intensity of the pulsations, 

 which were at their height on the eighth day, 

 and now gradually grow less. The allantois 

 covers a large part of the yolk-sac, and is ex- 

 tremely vascular, especially its upper layer 

 which lies close under the shell membranes. 

 The yolk is beginning to diminish rapidly, 

 and the yolk-sac is becoming wrinkled and 

 flabby. The little sacs containing the feathers 

 begin to protrude from the surface, especially 

 along the back, of the rapidly growing embryo. 

 On the tip of the nose is seen a chalky patch, 

 the beginning of the horny beak. 



The eleventh day to the time of hatching. 

 — By the eleventh day, the abdominal walls, 

 though much less firm than those of the chest, 

 may be said to be fully formed, and the loops 

 of the intestines which have been hanging 

 down loosely are enclosed in the body-cavity. 

 The body is thus completed except for the 



