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The fibrous membrane forming region of the isthmus of the oviduct of Gallu8 Dome8ticu8 forms the upper two thirds of the anatomical isthmus. The secreting surface of the isthmus is arranged in a series of longitudinal ridges. The mucous membrane consists of a surface epithelium of columnar cells beneath which is a layer of tubular glands. In the membrane forming part of the isthmus the tubular gland cells are filled with prominent secretory granules, hence the name granular isthmus. The tubular glands of the lower third of the isthmus have few prominent granules and the region has a characteristic reddish tinge; hence the name red region of the isthmus is appropriate.In the granular isthmus there are three types of surface epithelial cell. Scott, 1935]. The red region adds water, potassium and glucose to the egg white and is involved in the initial nidation mechanism of calcification prior to the hard shell formation in the pouch of the shell gland [Draper, 1966;Davidson and Draper, 1969; Simkiss, 1968]. Richardson [1935] gives the total length of the isthmus as 8 cm in his hens and includes the red region as part of the shell gland. This has caused some confutsion in discussions of the contribution of the isthmus and the shell gland to the egg respectively.The primary object of this investigation is the study of the structure of the granular isthmus in relation to its production of the form and the substance of the shell membranes. Table I gives the status of each of the oviducts examined, and in all over 100 blocks were examined from the isthmus region. METHODSBirds were prepared for E.M. studies by giving a lethal injection of Nembutal Shell membranes for study were obtained from eggs midway down the granular isthmus (hens 12 and 13), from a soft egg in the proximal part of the shell gland (hen 14), and from laid eggs following removal of the hard shell. Tissues remained in fixative for 1-2 hr, were rinsed in buffer solution for 2-3 hr and then post-fixed in buffered osmium tetroxide for 14 hr. They were then rinsed in buffer solution and dehydrated through a series of alcohols commencing with 50% alcohol. Propylene oxide was used to clear the tissues which were then soaked in a mixture of propylene oxide and Araldite before the main immersion in Araldite. The tissues were embedded in Araldite in flat trays or propylene pre-shaped capsules. For location purposes, 2 ,um sections were cut from the Araldite blocks and stained by azure blue 11 in sodium borate solution using a hot plate to facilitate staining. Thin sections were cut on an L.K.B. ultrotome, mounted on uncoated grids and stained with uranyl acetate followed by lead citrate [Reynolds, 1963]. Specimens were examined with a Philips E.M. 200 electron microscope.For histological and histochemical studies, oviducts were removed from birds which had been killed with intravenous Nembutal. Each was transferred to ice cold Tyrode's solution, dissected free of ligaments and connective tissue and everted over strips of Perspex. After fixation in 10% buffere...

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The mucous membrane of the infundibulum and magnum of the hen's oviduct is modified for the receipt and fertilization of the yolk and the elaboration of the bulk of the solid material making up the white of the egg. The secreting surface is arranged in a series of ridges which are particularly elaborate in the neck region of the infundibulum. The surface is lined with columnar epithelial cells and there is a sub-epithelial layer of tubular glands. There are two types of epithelial cell; ciliated, with little evidence of secretory activity; and granular, with the intracellular structure of a glycoprotein secreting cell. In the infundibulum the granular cells have electron dense granules and the tubular glands arise as invaginations from the epithelium of the deep crypts between the mucosal folds. The gland cells are structurally similar to the epithelial granular cells and have a characteristically large infranuclear granular endoplasmic reticular (GER) space filled with homogeneous material of low electron density, probably representing storage of synthesized protein. In the magnum the granules of the epithelial cells are of low electron density and fill the whole of the distended granular cell in the lower magnum, compressing the neighbouring ciliated cells.Three types of tubular gland cell are described in the magnum: Type A, filled with electron dense granules; Type B, filled with large masses of homogeneous material of low electron density; and Type C, occupied by GER cisternae together with a large and prominent Golgi area. The C cells, which are found in the magnum immediately after the passage of the egg, are regarded as the recovery phase of A cells which have discharged their granules on the passage of the egg. There is evidence that the dense granules of the A cells represent ovalbumin, the commonest protein of the egg white. The fibrous glycoprotein, ovomucin, with its large carbohydrate component, is probably produced by the granular cells of the magnum epithelium. There is a partial discharge of the secretion of the cells of the mucous membrane in response to the presence of the yolk. The nature of the secretion and the origin of some other components are discussed.The oviparous oviduct is unique among organs in that it is a sequence of at least four exocrine glands which secrete complex protein systems, carbohydrates and ions around a descending yolk. The intracellular synthesis and secretion which occurs in the oviduct during the phases of the 24-hr egg production cycle can readily be studied in a modern high production hen. Such a hen may produce as many as thirty consecutive eggs before pausing. The purpose of this investigation is to describe the ultrastructure of the various cell types making up the mucosa and the changes which occur in these cells during the secretory activity induced by the passage of a forming egg.Surface [1912] made a detailed study of the histology of the oviduct which was extended by Bradley [1928]. However, Richardson's account [1935] remains the standard work in this...