The study was undertaken to investigate the phenomenon of delayed embryonic development in the fruit bat Cynopterus sphinx. The study showed for the first time the slowed embryonic development in this species during gastrulation stage. The period of delayed development showed a relatively low circulating progesterone concentration due to decline in the corpus luteum function. Exogenous progesterone treatment however, failed to accelerate embryonic growth. The result of this study showed for the first time that the period of retarded embryonic development in C. sphinx coincides with...