No abstract

Information on the pre-hatching development of the platypus, Ornithorhynchus anatinus, is reliant on a small number of specimens, whose precise age is unknown. Material collected for J. P. Hill and now housed in the Hubrecht International Embryological Laboratory, Utrecht, contributes a major source of specimens. This paper presents new observations on developmental stages from the Hill collection, which allow for a more complete description of pre-hatching development.A feature of the pre-embryonic development of the platypus is the incomplete meroblastic cleavage. A column of ¢ne yolk spheres extends from beneath the embryonic blastodisc towards the centre of a yolky vitellus, as seen in birds.The major expansion of extra-embryonic membranes occurs after the formation of the primitive streak. The primitive streak develops within an embryonal area as part of the super¢cial wall of the yolk-sac, a feature also shared with marsupials, birds and reptiles.The full-term, subspheroidal, intrauterine egg of the platypus has a major axis of about 17 mm and contains a £at, 19^20 somite, neurula-stage embryo which has prominent trigeminal ganglion primordia. The embryo at this stage is in a period of rapid modelling of the major early organ primordia of the nervous system, cardiovascular system, excretory system, and somite-derived components of the body wall.Soon after laying, ¢ve primary brain vesicles are present, the trigeminal ganglia CN5 as well as CN7, CN8, CN9, CN10, CN11 and CN12 are well developed. The alimentary system has an expanded stomach, pancreatic primordia and a gall bladder. Mesonephric tubules are associated with patent mesonephric ducts, which empty laterally into the cloaca. Extra-embryonic membranes at this stage show an extensive chorioamniotic connection that extends through the greater part of the caudal half of fused amniotic folds. The vascularized yolk-sac consists of a super¢cial yolk-sac omphalopleura and a deep yolk-sac splanchnopleure. The non-vascularized yolk-sac comprises one-quarter of the abembryonal pole.Some distinctive monotreme features have developed by the mid-incubation period. The head is bent at an acute angle to the main body axis. The blunt upturned snout marks the site of the future oscaruncle and on the maxilla there is a median primordial papilla representing the egg tooth. The eye is open with a partly pigmented retinal ring. The forelimbs have partly separated digits, and the hindfeet are paddles. Just before hatching the upturned snout contains an oscaruncle and a sharp recurved median egg tooth. Forelimbs are pronated with separate digits possessing claw primordia. Portions of the highly vascularized extra-embryonic membranes are attached to the umbilical region and the £attened vesicular allantois has a distal region fused with the chorion.Prominent features of the hatchling are the presence of a bluntly conical oscaruncle and a translucent, horn-like egg tooth. These structures are thought to enable the hatchling to extricate itself from the egg shell. At hatchin...

This paper considers many of the salient features of monotreme development, particularly morphogenesis of the extraembryonic membranes. The uterine endometrium of both monotremes and marsupials exhibits a progesterone driven luteal phase where accelerated utilization of endometrial nutrients is evidenced by a rapid post-primitive streak expansion in the dimensions of the extraembryonic membranes. Monotremes share with marsupials, birds, and reptiles an unspecialized vertebrate mode of genesis of the embryonic disc on the peripheral surface of the yolk-sac. The fused vascularized respiratory chorioallantois is estimated to have a functional life of not more than the terminal 4 to 5 days of the monotreme incubation period. This time interval is of a slightly greater order of magnitude than that found in marsupials with a fused chorioallantois, so far described, but in the context of the proportional elapse of post-primitive streak organogenesis would fall within the marsupial grade. The dominant extraembryonic membrane for nutritive and respiratory function in both monotremes and marsupials is the yolk-sac. This contribution shows that monotremes and marsupials share a much larger suite of developmental anatomical features than previously reported. The evolutionary biologist is confronted with the challenge of how to assign an appropriate weighting to these features as marsupials are considered by many researchers to be allied phylogenetically more closely with eutherian mammals than with monotremes.

No abstract

The reproductive tracts of males from eight species of Australian marsupial were examined (Macropus eugenii, Potovous tridactyhs, Sminthopsis crassicaudata, Antechinus stuartii, Pseudocheirus peregrinus, Trichosurus vulpecula, Isoodon macrourus, and Perameles nasuta). The prostate glands of these species were found to be of two shapes, carrot-like or heart-like. From one to three pairs of Cowper's glands were observed; these were mostly bulbous in shape but some were kidney-shaped. Both prostate and Cowper's glands were tubular in structure with the glandular tubules lined by a simple columnar epithelium. The glandular tubules of Cowper's glands were of much larger diameter than those of the prostate. The prostate glands were segmented, and this segmentation was usually shown by variations in the height and staining reactions of the tubular epithelium and in the volume of connective tissue between glandular tubules. Differences in microanatomy between pairs of Cowper's glands were far less than those between prostate segments. Mucosubstance appeared to be the major contribution of the prostate to the seminal plasma. This mucosubstance was mainly neutral, with glycogen largely absent. The present results indicate that the Cowper's glands secrete mucus but that various glands also contributed lipid and glycogen.

Within the rostral one centimetre of the Echidna beak, three specialised receptors were found: a mucous sensory gland, a rod-like structure, and an innervated epidermal pit. The mucous sensory gland consists of a dermal mucous gland and a modified epidermal portion. Bulbous nerve terminals, similar to those reported for the Platypus, were found within the modified epidermal portion of the mucous gland. The rod-like structure contains four types of nerve terminals: Merkel cells, Paciniform corpuscles, and a central and a peripheral vesicle chain receptor. Apart from minor differences, the rod-like structure is similar to that previously reported for the Platypus. Preliminary results are presented for a third structure: an innervated epidermal pit. Topographical and ultrastructural analyses are used in the context of functional interpretation.

The proliferation and secretory activity of the uterine endometrium in the marsupial T. vulpecula is examined at the cellular and subcellular levels throughout the 26-day oestrous cycle. The observations described are correlated with measured concentrations of progesterone in the peripheral blood plasma. Evidence cited indicates that there are no significant functional differences in the uterine endometrial secretory activity during the 17.5-day gestation period in pregnant females, compared with those in a normal oestrous cycle. Progesterone assays carried out on blood plasma taken from 20 staged animals throughout the oestrous cycle, five of which were at known stages of gestation, also supports the view that pregnancy does not significantly alter the physiological pattern of the reproductive cycle in this marsupial.

The spermatozoa of 18 marsupial species derived from five families have been examined and of these only the spermatozoon of the bandicoot Perameles nasuta has previously been described adequately. The spermatozoon morphology within the families Macropodidae, Dasyuridae, Phascolarctidae, and Peramelidae was relatively homogeneous. A distinctive morphology occured between these families. Within the family Phalangeridae spermatozoa were morphologically diverse, however, as a group they were relatively separate from those of the other families studied. The spermatozoa of the Phascolarctidae (koala, Phascolarctos cinereus, and wombat, Phascolomis mitchelli) have a unique, somewhat rat-like morphology which clearly separates them from those of the other marsupial sperm studied. This finding is of considerable taxonomic interest as most authorities consider the koala to be more closely related to the phalangerid marsupials than to the wombat.