Fig. 7O2. Diagrams to illustrate the development of the 



embryo -with its yolk-sac, amnion, and allantois. 



(From Hertwig's 'Embryology.') 



a. External germinal layer, mw. Medullary groove. JV. Neutral canal, af. Amnion fold. vaf. 

 Anterior, haf. Posterior, saf. Lateral amniotic folds. A. Aranion. ah. Amniotic cavity. S. Serous 

 covering, hn. Umbilicus, sf. Lateral folds. kf l , kf. Head fold. a/6. External, ifb. Internal layers 

 of amnion. ur. Border of embryonic area. dr. Intestinal groove, dg. Vitelline duct. al. Allantois. 

 ds. Vitellus. dn. Intestinal portion of umbilicus, mk. Middle germinal layer. mk l . Parietal leaf 

 of mesoderm. mk''. Visceral leaf of mesoderm. st. Sinus terminalis. dm. Dorsal, vm. Ventral mes- 

 enterium. Ih. Somatic cavity. Ik 1 . Embryonal portion. Ik*. Extra-embryonal portion of somatic 

 cavity. Figs. 1, 2, 6, 8, 9, and 10 transections. Figs. 3, 4, 5, 7, and 11 longi-sections of embryo. Figs. 

 1, 2, 3, 4, and 5 chick embryo. Fig. 6 fish embryo. Figs. 7 and 11 selachian embryo. 



