The oogamous organisms are those who practice the oogamy form of reproduction. The oogamy is a form of heterogamy (the male and female gametes are different) where the female gamete is much larger than the male gamete. In such organisms, the female gamete (egg cell) is produced in smaller number while the male gametes (sperm cells) are produced in much larger numbers.
Hence, the blanks can be filled with 'egg and sperm' respectively.