558 



ZOOLOGY 



SECT. 



-^ =a= = ci ^ S^i 



^ftrrf^ 



ch 



FIG. 1149. -Five diagrammatic sections illustrating the formation of the foetal membranes 



of a Mammal. In 1, 2, 3, 4 the embryo is represented in longitudinal section 1 Ovum 

 with zona pcllucida, blastodermic vesicle, and embryonic area ; 2, ovum with commencing 

 formation of umbilical vesicle and amnion ; 3, ovum with amnion about to close 4 ovum 

 with vilkms Bubzonal membrane, larger allantois, and mouth and anus; 5, ovum in 'which 

 the niesoderm of the allantois has extended round the inner surface of the subzoinl mem 

 brane and united with it to form the chorion ; the cavity of the allantois is aborted 

 (/.ectoderm of embryo; ', ectoderm of non-embryonic part of the blast. >dermie vesicle" 

 ./,. anmiotic cavity ; at. allantois ; am. amnion ; d,. chorion; chz, churinnic villi </ zona 

 radiata; <!'. processes of x.ma ; .(,/, embryonic endoderm ; <//. area vasculosa: da, stalk of 

 umbilical vesicle ; ds, cavity of umbilical vesicle; e. embryo ; M, pericardial cavity: ; non- 

 embryomc endoderm; Kh, cavity of blastodermic vesicle ; A'*, head-fold of amnion' ,/) em- 

 bryonic mesoderni ; m. non-embryonic mesoderrn ; /, space between clmrion and amnion 

 sh, subzonal membrane ; , tail-fold of amnion ; at, sinus tcrminalis ; vl. ventral body wall' 

 (From Balfour, after Kolliker.) 



