ttmb.cL 



FIG. 164. Diagram illustrating the development of foetal membranes in a 

 bird. A, early stage in the formation of the amnion, sagittal section; B, slightly 

 later stage, transverse section; C, stage with completed amnion and commencing 

 allantois; D, stage in which the allantois has begun to envelop the embryo and 

 yolk-sac. The ectoderm is represented by blue, the endoderm by red, and the 

 mesoderm by gray, all, allantois; all', the same growing round the embryo and 

 yolk-sac; am, amnion; am. f, am.f, amniotic fold; an, anus; br, brain; coel, coelom; 

 coel', extra-embryonic ccelom; h, heart; ms.ent, mesenteron; mih, mouth; nch, 

 notochord; sp. cd, spinal chord; sr. m f , serous membrane; umb. d, umbilical duct; 

 vl, m, vitelline membrane; yk, yolk-sac. (From Parker and Haswell.) 

 320 



