Ptenochirus jagori (Megachiroptera, Pteropodidae) is a tropical cynopterine fruit bat restricted to the Philippine islands. Samples of bats were obtained over 4 years, and reproductive tracts were preserved and examined using standard histological techniques. Reproductive status also was recorded for bats captured, marked. and released. A facultative post-implantational delay in embryonic development was detected in young P. jagori females reproducing for the first time. The delay occurred at the stage of gastrulation and could last up to 5 months. Adult females showed little evidence of a delay in development. With this delay, young females gave birth only once in their first year and synchronized parturitions with those of adults. Adult females had a gestation period of 4 months and gave birth twice a year, once in late March and early April and once in August. Morphology of early development was similar to that of other cynopterine fruit bats. The evolution and significance of a post-implantational delay in development are discussed.

The endoplasmic reticulum (ER) is a dynamic organelle central to many essential cellular functions. It is an important calcium store, which functions in cellular signal transduction cascades. It is also the site of entry for secreted proteins into the secretory pathway. Lumenal enzymes will fold and glycosylate these proteins, and if a protein is destined to be secreted, it will be packaged into membrane vesicles that bud off from the ER. The ER is also the site where most cellular lipids are synthesized. It is contiguous with the nuclear envelope, which serves as a diffusion barrier to control entry into and out of the nucleus. In the life cycle of a cell, the ER is in a constant flux of membrane traffic. What maintains the ER in the shape of an intact reticulum among this constant flux of material? We discuss the mechanisms that contribute to the biogenesis of the ER, the maintenance of the organelle, as well as processes that give the ER its characteristic shape and pattern of inheritance.