In this paper taxonomic study on paragonimus including their metacercariae obtained from the crabs collected from Sorsogon, Luzon, Philippines and adult worms and ova obtained through animal feeding, with light microscopy and scanning electron microscopy revealed that there may exist two or more species of lung flukes in Philippines. The occurrence of Semisulcospira libertina in addition to Antemelania dactylus (Lea) as an additional snail host is mentioned for the first time. The chromosome Karyotyping of the adult worms revealed that they belong to the diploid pattern. Electronic scanning showed that the cuticular spines of the Paragonimus from Sorsogon look like "pineapple ears" both in distribution and in appearance, a new finding that has not been recorded before. In the lungs of a white rat killed 290 days after infection, two adult worms were obtained within the solitary cyst. These 2 adult worms measured 4.5 x 2.5 mm and 4.5 x 3.0 mm respectively. Their unusually small size and somewhat round shape suggest that they may be of a different species from those hitherto reported in the Philippines. Clearcut evidence is presented for the first time, demonstrating the occurrence of the phenomenon of cross fertilization (allogamy) of lung flukes.