ABSTRACT
The chicken chorioallantoic membrane is assessed between days 7 and 20 of incubation using light and electron microscopy with morphometric analysis. The completion of its formation by the middle of embryogenesis is observed, after that a rapid increase in the embryo body mass continues. The bloodstream combines chorionic epithelium, mesoderm, and allantoic epithelium into the single multifunctional organ. The ordered antiparallel arrangement of afferent and efferent vessels within the mesoderm as well as their specialized endothelium assist in partial blood fluid filtration into the interstitium. The unique structure of the capillary network within and over the chorionic epithelium that provide for the effective gas exchange is depicted. It is revealed that the ultrastuctural specialization of the chorionic epithelial cells through which an active calcium transport from the eggshell takes place. The ultrastructure peculiarities of the allantoic epithelium concerning the water-salt balance maintaining in the growing embryo, are discussed.
