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Summary.

The uterine luteal phase in T. vulpecula is not dependent upon the secretions of the CL throughout its duration. Ablation of the CL or ovariectomy after Day 7 of the 26-day oestrous cycle does not result in the termination of the uterine secretory phase. The dependence of the luteal phase on the secretions of the CL is demonstrated by ablation of the CL or ovariectomy on Days 2, 4, 8, 12 and 24 of the oestrous cycle. Ablation of the CL before Day 8 resulted in the inhibition of the impending luteal phase, and the commencement of a follicular phase resulting in oestrus 8 to 9 days later. Removal of the CL or ovariectomy on Days 8 or 12 does not completely inhibit the uterine luteal phase since sufficient precursor of uterine milk is stored in the uterine basal glandular epithelium, thus enabling the endometrium to maintain the secretion of uterine milk.

Summary.

The permeability properties of the shell membrane, mucoid coat, zona pellucida and vitelline membrane of thirteen Trichosurus vulpecula eggs were investigated by incubating them in a mixture of the animal's own blood plasma and one of the following substances : vital toluidine blue (mol. wt. 306) ; horse radish peroxidase (mol. wt. 40,000) ; ferritin (mol. wt. 460,000). The degree of penetration of these tracers was assessed either with the light microscope or electron microscope or both.

Both toluidine blue and peroxidase penetrated the shell, the mucoid coat and the zona pellucida to enter the vitellus within 5 min. In eggs with fully formed shell membranes and mucoid coats, ferritin particles penetrated the superficial portions of the shell in low concentrations. There were fewer particles in the deeper portions of the shell and, in the mucoid coat, they were extremely rare or absent. In eggs either lacking a shell or with a thin newly formed shell, ferritin infiltrated the zona pellucida. It was concluded that the pore size of the shell was such that some filtration of ferritin was occurring. Because of the penetration of substances with such a large molecular weight as ferritin and peroxidase, it was considered that neither the shell, the mucoid coat nor the zona pellucida was significantly involved in regulating the passage of embryonic nutrients or wastes.

Summary. Observations were made using scanning and transmission electron microscopy and were correlated with measurements of the mean surface area and the percentage area occupied by secretory cells to provide precise interpretation of the morphological data.

In cyclic and anoestrous possums the oviducts were lined with elaborate folds of mucosa except in the portion of the isthmus adjacent to the uterus where the pattern was much simplified. The folds decreased in height and number after ovariectomy. Secretion was maximal between oestrus and Day 2 of the cycle when most ovulations take place. Extrusion of vesicles was observed in the ampulla and isthmus at this stage although the process was localized to some extent because groups of cells with actively extruding vesicles were interspersed with others which contained vesicles but otherwise appeared inactive. This is interpreted as a device whereby a constant supply of secretion can be maintained over several days. Secretory activity declined between Days 3 and 8 and the epithelium in mid-cycle (Days 8–18) appeared relatively quiescent. By Day 24 there was morphological and morphometric evidence of a return to oestrous conditions, although vesicles had not yet reappeared in secretory cells. Ciliogenesis was prevalent at this time and is probably related to the ovum transport that will occur several days later.

Summary. Morphology and morphometry of the luminal surface of the uterus of the brush-tailed possum were studied during the oestrous cycle, in anoestrous animals and after ovariectomy.

At oestrus the secretory cells were small and the epithelium heavily ciliated. The relative surface area occupied by secretory cells reached a maximum on Day 13 when plasma progesterone concentrations are maximal. The mean apical surface area of the secretory cells also reached a maximum at this time. Both these measures decreased on Day 18 when involution of the epithelium was taking place. This process was essentially complete by Day 24 and was followed by extensive ciliogenesis.

Secretory cells from anoestrous animals appeared to have an apical surface area similar to the minimum recorded during the oestrous cycle and extensive loss of cilia did not occur. Ovariectomy caused loss of ciliated cells and a reduction in the mean apical surface area to a dimension much smaller than that measured in intact animals.