M 



a.m. 



'if 



FIG. 1016. Diagrams illustrating the development of the foetal membranes of a Bird. A, early 

 stage in the formation of the amnioii, sagittal section ; B, slightly later stage, transverse section ; 

 C, stage with completed amnioii and commencing allautois ; D, stage in which the allantois has 

 begun to envelop the embryo and yolk-sac. The ectoderm is represented by a blue, the eiidoderm by 

 a red line ; the mesoderm is grey. all. allantois ; all', the same growing round the embryo and yolk- 

 sac ; am. amnion ; am.f., am.f.' amniotic fold; an. anus ; br. brain; ccel. co^lome ; ccel'. extra-em- 

 bryonic ccelome ; lit. heart ; ms.ent. mesenteron ; mth. mouth ; nch. notochord ; */>. cd. spinal cord ; 

 sr. m. serous membrane ; umb. d. umbilical duct ; rt. m. vitelline membrane ; i/k: yolk-sac. 



