Development of the Second Day i6i 



ment as the head-fold. As will be seen by 

 examination of Figs. 37 and 38, the space be- 

 tween the two layers of the amnion (dotted in 



^•V^^g 



pro.aiQ, 



P'iG. 55. — Transverse section through a chick embryo, to 



SHOW A SLIGHTLY LATER STAGE IN THE DEVELOPMENT OF THE 

 HEART THAN IS SHOWN IN FiG. 48. (After Minot.) 



Md^ wall of medullary tube, nch^ notochord. msihy mesothelium, /%, 

 pharynx, pro. avzy tip of pro-amnion. en.kt^ endothelial heart, m.ht^ muscular 

 heart. 



Fig. 37) is continuous with the body or pleuro- 

 peritoneal cavity. 



The allantois may make its appearance be- 

 fore the close of this day, but it will be better 

 to defer its description until the following day's 

 development is discussed. 



