Observations on the chorioallantoic placenta of the Indian flying fox, Pteropus giganteus giganteus.

The present study was undertaken to resolve (1) whether the interhaemal membrane of Pteropus giganteus at term is endotheliochorial or haemochorial and (2) how the trophoblast is layered. Females carrying late limb bud stage (CRL 12.95 mm) and advanced fetus (CRL 26.95 mm) were collected at Nagpur, India. The placenta in late limb bud stage was examined by light microscopy and that of advanced pregnancy by both light and electron microscopy. Our observations reveal that the chorioallantoic placenta at late limb bud stage is horse-shoe shaped and endotheliodichorial while that of advanced pregnancy is mesometrial, labyrinthine, and discoidal and shows a tendency toward becoming haemochorial. The junctional zone contained multinucleate giant cells. Detached endothelial cells were observed in the maternal capillary lumen during the advanced stage. Under light microscope a thick homogeneous layer was noticed deeper to the endothelial cells and in the regions devoid of such cells. A PAS-positive, highly reticulate and discontinuous interstitial membrane was noticed embedded in the thickness of the homogeneous layer. The ultrastructure of the interhaemal membrane of the chorioallantoic placenta in advanced pregnancy shows a tendency from endotheliodichorial to haemodichorial condition. The Pteropus interhaemal membrane is compared with that of bats of other families. The earlier conclusion that the maternal endothelium is typically different for primitive and extant families is denied on the basis of comparative ultrastructure.

Development of the vomeronasal organ in Rousettus leschenaulti (Megachiroptera, Pteropodidae).

A functional vomeronasal organ (VNO) is known to be lacking in adult bats of the suborder Megachiroptera, family Pteropodidae, studied to date. However, whether the VNO every forms during ontogeny in megachiropterans has not been addressed. We report here on the development of the VNO in megachiropterans via study of 8 stages of rousette fruit bat Rousettus leschenaulti, ranging from an early limb bud embryo to a young specimen attached to the nipple. A vomeronasal primordium appears in the 4 youngest stages (7-14 mm crown-rump length), but there is no sign of any of the components of the vomeronasal system (neuroepithelial tube, nerves, sinuses, glands, or trough-like cartilage) in the septal region of the 4 oldest stages examined, or in the adult. Given the number of genera investigated to date and their taxonomic diversity, a conclusion that a VNO is entirely lacking in Megachiroptera seems reasonable. However, final confirmation awaits study of the additional 27 genera not yet reported (out of a total of 41).

Reproduction in the Indian mouse-tailed bat, Rhinopoma hardwickei hardwickei (Chiroptera, Rhinopomatidae).

At and near Agra, in Uttar Pradesh, India, R. h. hardwickei had a strictly defined annual reproductive cycle. Although many females were inseminated during late February to mid April, ovulation was not recorded until 11 March. Progressively more females ovulated and conceived during the following weeks until the end of April and released one ovum from either of the ovaries with nearly equal frequency. A single conceptus was carried in the ipsilateral uterine cornu during each cycle. The gestation period was 95-100 days. Births occurred between the second week of June and the end of July. Lactation lasted at least 20 days. Females attained sexual maturity at an age of 8.5-9.0 months. Males took at least 16-17 months to attain sexual maturity. Females were segregated during lactation; during the rest of the year, males and females lived together.

Early embryonic development and preimplantation changes in the uterus of the bat Rhinopoma hardwickei hardwickei (Gray) (Rhinopomatidae).

Rhinopoma hardwickei hardwickei has an annual reproductive cycle. Although many of the females become inseminated from the latter half of February until about the middle of April, ovulation has not been recorded until the 11th of March. A single follicle reached full development and released one ovum from either of the ovaries with nearly equal frequency, and a single conceptus was carried in the ipsilateral uterine cornu during each cycle. The embryo descended into the uterus as an early morula and attained the bilaminar blastocyst stage before undergoing implantation. As the morula advanced in age, the embryonic surface of the zona became progressively more basophilic. Hence in advanced morulae, the inner surface of the zona pellucida took a dark stain with hematoxylin and appeared like a distinct thin membrane, while the rest of the thickness of the zona was eosinophilic. Although progestational changes commenced in both uterine cornua, they became augmented in the uterine cornu on the side of ovulation and blastocyst attachment. After blastocyst attachment, the contralateral cornu reverted to an anestrus condition. The progestational changes became less conspicuous from the cranial to the caudal end of the uterus. Evidently, there was a linear gradient in the progestational response of the uterus with the cranial end being most responsive and the caudal end least responsive. The precise mechanism which brings this about is not known.

Ultrastructure of the pineal gland of the tropical bat Rousettus leschenaulti.

The ultrastructure of the pineal organ was studied in the tropical megachiropteran Rousettus leschenaulti. The pineal lies deep beneath the hemispheres adjacent to the third ventricle and is traversed by the habenular commissure anteriorly. Its parenchyma consists of a uniform population of light and occasional dark pinealocytes which appear to differ only in the degree of cytoplasmic staining. Pinealocytes are characterized by well developed Golgi bodies associated with numerous small vesicles, many mitochondria and polyribosomes, and frequent subsurface cisternae. Lipid droplets and elements of smooth endoplasmic reticulum are scant. Cisternae of granular endoplasmic reticulum are occasionally dilated. A distinct feature is the abundance of clear vesicles in the pinealocyte pericapillary terminals, which also frequently contain granular vesicles and a very large vacuole. The pineal is further characterized by the presence of a small number of glial cells and myelinated nerve fibers. A broad perivascular space investing numerous capillaries contains glial-cell and pinealocyte processes, collagen fibrils and abundant unmyelinated nerve fibers. Tortuous extensions of the perivascular space enter the pineal parenchyma where they come in close proximity to branched intercellular channels or canaliculi characterized by specialized junctions and microvilli. Differences between the pineal of the non-hibernating megachiropteran Rousettus and that of the hibernating microchiropteran bats, and structural similarities to the pineal of tropical rodents are discussed.