226 



EMBRYOLOGY. 



Fig 182. Five diagrammatic figures illustrating the development of the foetal egg-membranes 



of a Mammal, after KOLLIKER. 

 figures 1 to 4 the embryo is represented in longitudinal section. 



(1) Ovum with zona pellucida, blastula, embryonic area, and embryonic fundament. 



(2) Ovum in which the yolk-sac and the amnion are beginning to develop. 



(3) Ovum in which, by the fusion of the amniotic folds, the amniotic sac and the serous mem- 

 brane are formed, and the allantois makes its appearance. 



(4) Ovum with serous membrane, which has developed villi, with a large allantois and an 

 embryo, in which the t>ral and anal openings have arisen. 



(5) Diagrammatic representation of a young human ovum, in which the vascular layer of the 



allantois has become applied to the serous membrane on all sides, and lias grown into its 

 villi. The serous membrane from this time forward takes the name of chorion. The cavity 



