co — folds, forming the heart; co — the vessel layer covering 



the yolk; f — the upper layer of the head portion. (15) 



Longitudinal section made in the amnion of the fetus : 



aa — external side of the primary folds; oc — lateral parts 



of the fetus; ee — serous layer of the blastoderms forming 



the false amnion; h — opening which later closes; ff — internal 



layer of these serous layers (especially the amnion) ; 



g — opening by which the intestines are connected with the 



yolk; bb — blastoderm. P (16) Transverse section on the lines 



of (15) . The explanations are the same. 



250 



