Three individually different karyotypes were found in O. rubiginosus as follows: type I (male: 2n=24A+X1 + X2 + Y; female: 2n=24A + 4X), type II (male: 2n=22A + X1 + X2 + Y1 + Y2) and type in (male: 2n=20A + X1 + X2 + X3 + Y2 + Y2, or 20A + X1 + X2 + Y1 + Y2 + Y3). It seems probable that type II may be derived from type I through association of a pair of autosomes with the sex-chromosomes, and that type III is derived in similar manner from type II.