THE OOCYTE OF TRIPLOID FLUKE RECEIVING INTRUSION OF SPERM FROM A DIPLOID FLUKE - EVIDENCE FOR THE ORIGIN OF TETRAPLOIDS IN PARAGONIMUS-WESTERMANI

An experiment was conducted to elucidate the origin of tetraploids (2n = 4x = 44) of Paragonimus westermani that occur together with diploid (2n = 2x = 22) and triploid (2n = 3x = 33), types in Liaoning Provinc e, the People's Republic of China. Metacercariae of the diploid type, obtained from Hyogo Prefecture, Japan, and those of the triploid type from Tsushima, Nagasaki Prefecture, Japan, were mixed and inoculated I nto dogs and cats. The following results were obtained. The flukes wer e found in pairs within cysts in random combinations of 2x + 2x, 2x 3x, and 3x + 3x (7:15:7). Oocytes in the oviduct were at stages from d iplotene to metaphase. In a triploid fluke encysted with a diploid flu ke, the primary oocytes were intruded by sperms from the diploid fluke . In the primary oocytes of diploid as well as triploid flukes, from d iplotene to diakinesis, the homologues of the nucleolar chromosomes we re heteromorphic as far as the size of the short arm was concerned. Th is implies that the triploid is an autotriploid generated in an ancest ral diploid population that was polymorphic for the nucleolar chromoso me.