Follicular cell ultrastructure during chorion and corpus luteum formation was studied in supplementary reproductives of the termite Kalotermes flavicollis. During choriogenesis the follicular epithelium is formed by large flattened cells joined together by specialized junctions. Follicular cells have an extended rough endoplasmic reticulum (RER) with cisternae parallel to the cell long axis and many Golgi complexes surrounded by secretion vesicles moving towards the egg surface. At the end of choriogenesis the follicular cells move away from the just completed chorion and show few RER cistemae and scarce Golgi apparati. When the egg is ejected from the ovariole, the empty ovarian follicle collapses; the irregularly shaped follicular cells, now exhibiting in their cytoplasm small autophagic vacuoles and polymembranous structures, form the initial corpus luteum. This undergoes a further shrinking, becoming an ovoidal mass (the advanced corpus luteum) formed by irregularly shaped follicular cells containing numerous heterogeneous inclu- sions. The ultrastructural evidence rules out any hint of a functional activity of corpus luteum cells, but supports the hypothesis of their progressive degeneration. The chorion is made up of an endochorion with a trabeculate structure and a compact layer exocho- rion. The chorion surface is sculptured with polygonal plates which are follicular cell imprints. On the egg dorsal side, near the posterior pole, there is the micropylar region formed by several oval plates arranged in an arched pattern. On the same side, near the opposite pole, the preformed field for embryo hatching is found, made up of four rows of rectangular plates
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