The length of the oestrous cycle of the bandicoot Isoodon macrourus was determined. Pouch young were removed from lactating bandicoots at day 30 of lactation and the mothers were subsequently housed in enclosures without males (for oestrous cycle) and with males (for pregnancy). Births were observed 32-48 d after removal of young. The period of removal of young until ovulation was shown to be 6 d, the gestation length was known to be 12.5 d and the length of an oestrous cycle was calculated to be 22.1 1.6 d (mean s.e., N=10), with a range of 14-30 d.

Various morphological and physiological features were examined weekly in developing male bandicoots, each housed with a mature female, from birth through to the fathering of their first litter. The first peak of plasma testosterone greater than 2 ng ml-' in the male was observed at 179.8 6.8 d old (mean SE; n = 17); sperm were first observed in the male reproductive tract at approximately 200 d old and this coincided with the pigmentation of the scrotal skin at 199.5 8.2 d (n= 10). The first litters were sired at 349.7 14.0 d (n=7). Male bandicoots reached sexual maturity approximately 100 d later than females. Pigmentation of the scrotum would appear to be a useful indicator of the stage of sexual development because it occurs at the stage of development when sperm first appear in the reproductive tract in the male bandicoot. Nevertheless, the appearance of sperm and scrotal pigment, both precede sexual maturation by at least 150 d and are not good indicators of reproductive ability in the male bandicoot.

Reproductive activity is seasonal in bandicoots. To determine the seasonal changes in the reproductive tract of the male bandicoot, the morphology of the testis and the prostate was examined during the breeding and non-breeding season. Although the dimensions of the testes of the bandicoot did not change with season, the volume of testicular Leydig cell tissue increased about twofold and this change within the testis was accompanied by a threefold increase in prostate gland size. The bandicoot prostate can be divided into two zones, a dorsal zone which produces a carbohydrate secretion containing the enzyme acid phosphatase, and a smaller ventral zone which produces a mucoprotein secretion lacking acid phosphatase activity. These morphological changes within the testis and the prostate gland of the male bandicoot correlate with the seasonal variation in plasma testosterone concentrations previously reported. The testosterone concentration in the male starts to rise in May and reaches a peak in September and presumably causes the increase in prostate gland size and activity.

Melatonin implants were placed in 5 adult female possums during December. Births were observed from 31 March to 12 April in 4 control possums, and on 16 January, 1 and 6 February, 27 March and 27 April in the melatonin-treated animals. Melatonin would appear to have advanced the start of the breeding season in 3 of the 5 animals. Following removal of pouch young a subsequent birth is more likely to occur when young are removed early in the breeding season. These results would suggest that daylength may play a role in the initiation of the breeding season and the stimulus to mate diminishes from March through to September. Nevertheless, if the environmental conditions are favourable a secondary peak of births can occur in the later part of the year.

The concentration of progesterone in maternal plasma of the bandicoot increased from 3.9 to 12.6 ng/ml between 11 and 4 days before parturition and remained at this level for at least 7 days. Concentrations of 13,14-dihydro-15-keto-prostaglandin F-2 alpha increased from basal levels of 288 pg/ml (4 days before birth) to maximal levels of 2534 pg/ml immediately after parturition, then decreased progressively. It is suggested that PGF-2 alplha, but not progesterone, influences the initiation of parturition in this species.

The ultrastructure of the corpora lutea of lactation in the bandicoot I. macrourus has been correlated with the concentration of progesterone in the maternal plasma. The circulating level of progesterone declined from a maximum of 12.3 1.6 (SE) ng ml-1 (n= 11) early in lactation at days 0-10 post partum, to 4.1 0.4 (SE) ng ml-1 (n=25) at days 11-57. This change in hormone concentration is in accord with the loss of densely staining granules from the luteal cells.

The caudate lobe of the liver of normal sheep and of sheep poisoned by the plant Lantana camara L. was fixed by perfusion with a mixture of glutaraldehyde and paraformaldehyde. The tissues were prepared and then examined with a transmission electron microscope. It was concluded that ingestion of lantana is followed by closure of bile canaliculi and damage to microvilli and that these changes contribute to the decrease in bile secretion seen during lantana poisoning. A marked increase occurred in the agranular endoplasmic reticulum but the significance of this is not known. It may be related to alterations in the amount of drug metabolizing enzymes or to retention of bile constituents.

The development of subcutaneous and perirenal adipose tissue in foetal sheep of 40--150 days conceptual age was examined using electromicroscopy. Adipose tissue from both sites developed from pre-adipose cells of similar appearance, with few mitochondria, and commenced accumulating lipid on about day 70 of gestation. In the perirenal fat there was marked proliferation of mitochondria between days 80 and 90 and the tissue developed into brown fat, cell profiles being characterized by many mitochondria with numerous distinct cristae, whereas in the subcutaneous cells which developed into white adipose tissue few mitochondria with fewer cristae were observed. Multilocular and unilocular cells occurred in both tissues near term. Nerves were first seen between brown adipose cells in a 130-day-old foetus and were frequently seen in older foetuses, but very few nerves were seen in the white adipose tissue. In hypophysectomized foetuses, either full- or post-term, the subcutaneous fat and internal fat were shown to be white and brown adipose tissue respectively, as in normal foetuses, although in one 164-day-old foetus the perirenal tissue appeared to be a mixture of brown and white fat.

A correlative study of the ultrastructural and biochemical effects of ACTH on fasciculata cells was carried out on the isolated cat adrenal gland perfused in situ with Locke's solution. The outstanding morphologic feature of cortical cells exposed to microunit ACTH concentrations for 40 min was the abundance of electron-dense granules (0.2-0.4 mum). These organelles were observed in small groups in close proximity to the Golgi region and to the cell membrane. Morphometric and biochemical analysis of control and ACTH-treated glands demonstrated that ACTH stimulation was associated with a fourfold increase in the number of these granules and a comparable increase in the corticosteroid content of the gland. By contrast, ACTH failed to augment cortical lysosomal enzyme activity. These findings, which link steroid release to the appearance of intracellular granules, extend further the parallels between the mechanism of release of newly synthesized steroid and the release of preformed hormones stored in secretory organelles. These results also lend support to the concept that a process related to exocytosis may be the underlying mechanism for extruding steroid from the cortical cell.

The stomach of the tammar may be divided into cardiac, "oesophageal", fundic and pyloric regions. In the cells of the cardiac region (which occupy 65% of the stomach) at least three types of mucous droplet are present. The stratified squamous "oesophageal" region occupies 20% of the stomach and the fundic and pyloric regions make up the remaining 15%. The cellular structure of the three last named regions seems to be similar to that described for other monogastric mammals. Endocrine cells were found in all glandular regions.

Study of luteal regression in the sheep by electron microscopy showed that a characteristic sequence of degenerative changes defined the involution of the luteal cell at the end of the oestrous cycle (Gemmell, Stacy & Thorburn, 1976) and the same pattern of cellular disorganization was induced prematurely by administration of prostaglandin (PG) F-2α during the active, secretory phase of the cycle (Stacy, Gemmell & Thorburn, 1976). The present report describes the structural and functional changes in the corpus luteum (CL) following the infusion of an analogue of PGF-2α(ICI 80,996: Cooper, 1974) into the uterine vein of sheep.

In adult sheep, the hepatic sinusoids have an endothelial lining with numerous gaps and fenestrae and are surrounded by a complete basal lamina. In newborn lambs, the sinusoids have a relatively thick endothelium with fewer gaps, and the space of Disse contains a partially formed endothelial basal lamina. In both adult sheep and lambs, perisinusoidal cells appear to form a network around the sinusoid. In portal areas, the endothelium of the smaller capillaries is fenestrated, but the larger capillaries have unfenestrated walls and are enmeshed in processes of pericytes. Projections of endothelial cells partially or completely occlude the lumen of some portal capillaries, and of a large majority of sinusoids scattered throughout the lobule.