S8 



THE THIRD DAT. 



[chap. 



must not be confounded with the curvature of the body just 

 referred to) we have already seen was commenced in the 

 course of the second day, by the bending downwards of the 

 head round a point which may be considered as the extreme 

 end either of the notochord or of the ahmentary canal. 



?tB 



FB 





OfV 



Chick of the Third Day (54 hours) viewed from dndeeneath as a 

 Transparent Object. 



a . the outer amniotic fold or false amnion. This is very conspicuous around 



the head, but may also be seen at the tail. 

 a. the true anjiiiim, veiy closely enveloping the head, and here seen only between 



the piMJectious of the several cerebral vesicles. It may also be traced at 



the tail, t. 

 In the embryo of which this is a drawing the head-fold of the amnion 

 reached a little farther backward than the reference u, but its limit could not be 



