Association of epithelial nests with cortical vessels, oocyte-nest assembly and formation of CK18+ Balbiani body. A and B (copy of A with letters and dashed line) show the CK+ (brown color) nest body wall (w) inside of the cortical venule, which extends an arm (a) to catch the oocyte (o, dashed line) and move it outside of the blood vessel. C and D show the nest body and closing "gate" (g). A portion of the oocyte (dashed line) still lies outside of the complex, and is expected to move inside (arched arrow). The oocyte contains intraooplasmic CK+ (brown color) material (arrowheads). Extensions from the nest wall (arrows) contribute to the formation of CK+ paranuclear (Balbiani) body (asterisk). The oocyte nucleus is indicated by a dotted line. vl, vascular lumen; e, endothelial cells. CK18 immunostaining, hematoxylin counterstain.