Analysis of mitotic and meiotic chromosome spreads from testicular, ovarian and uterine tissue ofParadistomoides orientalisrevealed a diploid number of 28 for this species. The karyotype consisted predominately of biarmed chromosomes forming a gradual relative length series. Serial squashes of the oviduct and the proximal region of the uteri were used to follow chromosome behaviour at various stages of zygote formation. Based on these studies, early divisions of the oogonia were found to occur in the ovary whereas metaphase-1 spreads from the primary oocyte were observed in the ootype region. This region was also marked by the entry of the sperm into the ooplasm of primary oocyte. Once inside the egg, sperm chromatin formed fourteen thread like chromosomes termed as precondensed chromosomes. Primary oocyte pinched off 1st polar body nucleus followed by 2nd meiotic division. After releasing 2nd polar body nucleus, prophase chromosomes of the female pronucleus and precondensed chromsomes from the sperm nucleus passed directly in to metaphase of the first cleavage division. No fusion between male and female pronuclei was observed.