Cynopterus sphinx breeds twice annually in quick succession at Varanasi. The first pregnancy lasts for about 150 days and the second for 121 days. Data suggest that in C. sphinx retarded development of embryo during late November to early January accounts for the longer duration of gestation in the first pregnancy. Most interestingly noticed in the present dead cells within the inner cell mass during the period of retarded embryonic development. Cell death appears to cause the formation of the amniotic cavity by the cavitation process.