n8 Vertebrate Embryology 



the tail and lateral folds of the amnion. The 

 way in which these folds fuse together will be 



FIG. 38. C D DIAGRAMS ILLUSTRATING THE DEVELOPMENT OF 

 THE FCETAL MEMBRANES OF A BIRD. (After Parker and Haswell.) 



C, stage with completed amnion and commencing allantois. Z>, stage in which 

 the allantois has begun to envelop the embryo and yolk-sac. The ectoderm and 

 entoderm are represented by black lines ; the mesoderm is gray. 



a//, allantois. //', the same growing round the embryo and yolk-sac. 

 a tn, amnion. am.f, am.f, amniotic fold. , anus, br, brain. coel, 

 ccelome. coel', extra-embryonic crelome. h t, heart, ms.ent, mesenteron. 

 ntth^ mouth, nch^ notochord. sp.cd^ spinal chord, sr.m, serous membrane. 

 u mb.d, umbilical duct. vt,m, vitelline membrane, y k, yolk-sac. 



explained later, and will readily be understood 

 by study of Figs. 37 and 38. 



The formation of the allantois cannot readily 



