AbstractAn area under the ependyma of the infundibulum in jungle fowl hens enlarges progressively during incubation. The structure is reduced in size and altered in appearance in laying hens, regressed in nonlaying hens, and absent in males. Enlargement of the structure does not depend on increasing or decreasing day length. The area did not enlarge in jungle fowl receiving injections of prolactin. No similar structure was found in incubating house sparrows, rock doves, or ring‐necked pheasant.Histological and histochemical examination of the enlarged area led to the tentative conclusion that it may represent a neurohaemal depot for ergones from the infundibular hypothalamic nuclei and may be evolved from a structure homologous with the neurohypophysis of lower vertebrate