Isthmic and ampullary oviductal epithelia sampled from Merino ewes at days -1, 1, 3, and 10 of the estrous cycle (estrus = day 0) were studied by scanning and transmission electron microscopy after fixation by vascular perfusion. Secretory cells, ciliated cells, and lymphocytelike basal cells were observed in both isthmic and ampullary epithelium at all stages of the estrous cycle studied and their ultrastructural features were analyzed. Synthesis of lamellated secretory granules occurred in the ampullary secretory cells during the follicular and early luteal phases, and their contents were released by exocytosis into the oviductal lumen during the luteal phase. Granule release was associated with nucleated apical protrusion of these cells into the oviductal lumen. No such secretory activity was displayed by isthmic secretory cells even though a few cells contained nonlamellated granules. Apocrine release of apical vesicles and accompanying cytoplasmic material from apical protrusions of ciliated cells occurred in the isthmus around estrus but not in the ampulla. This unexpected feature has not previously been reported in any other mammal. Dendritic basal cells were distinguished in the lower part of the epithelium by their heterochromatic nuclei, electron-lucent cytoplasm, and lack of attachment zones. No migration of basal cells was observed, and their ultrastructural features were similar in the ampulla and isthmus and at all stages of the estrous cycle examined. The function of these lymphocytelike cells in the epithelium is uncertain, but the presence of phagocytic bodies and lysosomes in 20% of them may indicate a phagocytic role.

SummaryLight-microscope studies reveal distinctive features in the hair-and woolgrowing skin of adult sheep. The epidermis is variable in thickness-usually thin on wool-growing regions and thicker on haired regions. The follicles are mostly in groups containing one, two, or three primary (P) follicles and a number of secondary (S) follicles. The SIP follicle ratios vary from zero to about 30, depending on the breed and body region. The capillaries, myoepithelium of sweat glands, and dermal papillae of the follicles are often reactive for alkaline phosphatase. This enzyme is also asymmetrically distributed in some follicle bulbs and here it might be related in some way to the segmentation of the fibre cortex and perhaps to the formation of crimped wool. The dermal and follicle nerve networks contain cholinesterases. The latter may also contain alkaline phosphatase. Encapsulated end-organs and tactile disks are occasionally present in both hair-and wool-growing skin. Melanocytes, most common near the dermo-epidermal junction, may also be present in the outer root sheaths of the follicles, sebaceous glands, sweat glands, and dermis. Acetylcholinesterase-positive branched cells are invariably present in the epidermis in all regions where there are follicles. Sebaceous glands are associated with all follicles and apocrine sweat glands with the P follicles only. The P follicles also possess erector muscles that react for cholinesterases. Both the subaceous glands and sweat glands are usually larger in haired regions than in wool-growing regions. Large "eccrine" glands open on the naked part of the muzzle.

SummaryMacroscopic and microscopic changes in the skin of seven adult Suffolk and Merino sheep were studied for periods of up to 513 days following the application of solid carbon dioxide to hair-and wool-growing areas after clipping or plucking of the fibres. Observations were also made on the effect of plucking alone.A colour change from black to whit,e occurred in the coat subsequent to freezing skin which previously grew black hair in Suffolks and black hair or black wool in Merinos. In contrast, follicles which grew white wool in Suffolks and in an isolated white area on an otherwise "black" Merino sheep were induced to grow black or partially coloured fibres for periods ranging from a few days to several months when damaged by freezing the skin or plucking the fibres. The outer root sheaths of the follicles in the regions which normally grew white wool in these animals were the only source of the melanocytes which appeared near the dermal papillae of regenerating follicles and passed pigment into the new fibres. When the skin was frozen after the fibres had been plucked, the melanocytes in the follicle outer root sheaths were usually destroyed and the new fibres were non-pigmented.Other changes which frequently resulted from freezing the skin were an increase in the thickness of the epidermis, destruction of the sweat glands, a reduction in the number of follicles per unit area of skin, and a reduction in the innervation of the skin. No follicle neogenesis was seen. An increase in the length of the fibres, due either to an increased growth rate or to an increase in the duration of the growth cycle, sometimes occurred.

Twelve embryos, ranging from a four-celled stage to late unilaminar blastocysts, were obtained from the bandicoots I. macrourus and P. nasuta and examined by light and electron microscopy. These early stages covered at least one-quarter of the 12.5-day gestation period. The three non-cellular egg membranes characteristic of marsupials (zona pellucida, mucoid coat and shell membrane) were present, although the zona was sometimes absent or discontinuous in the intermediate and late unilaminar blastocysts examined. At the four-celled stage the blastomeres were close to the zona, but they had lost contact with each other, probably due to the extrusion of yolk, a phenomenon which has been described in other marsupials. The embryo did not increase in diameter until it was composed of at least 75 contiguous cells, which were in contact with the zona. In several of the larger blastocysts the protoderm cells had lost contact with the zona. Subsequently, the number of cells increased considerably and they were flattened against the egg membranes to form the late unilaminar blastocyst stage. Electron microscopy of the protoderm cells revealed the presence of numerous microvilli, particularly on the outer surface, and a range of other structures as great as those found in eutherian mammals. Remnants of spindle bridges were common in one 75-celled embryo. The yolk material in the blastocoele was also composed of a variety of structures, including small crystalloid inclusions composed of hexagonal units about 8-10 nm in diameter. Similar crystalloids have been described in the cells of early mouse and rabbit embryos and in egg and embryonic cells of various amphibians.

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