5r 



' 



all 



FIG. 1089. Diagrams illustrating the development of the foetal membranes of a Bird. A, 

 early stagein the formation of the amuion, sagittal section ; B, slightly later stage, trans- 

 verse section ; 6', stage with completed amiiion and commencing allantois ; D, stage in 

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

 represented by a blue, the endoderm by a red line ; the mesoderm is grey. all. allantois ; 

 all', the same growing round the embryo and yolk-sac ; am. amnion ; arn.f., am.f. amniotic 

 fold ; an. anus ; br. brain ; ccel. coalome ; ccel'. extra-embryonic ccelome ; ht. heart ; ms.ent. 

 mesenteron ; mth. mouth ; nch. notochord ; sp. cd. spinal cord ; sr.m. serous membrane ; 

 umb.d. umbilical duct ; vt.m. vitellme membrane : yk. yolk-sac. 



