Bradhionus plicatilis was successively cultured to the 3rd generation in low (1 individual/10ml) or high (1 individ./0.1 ml) density condition individually. In the previous report these experimental conditions induced significant difference in the inductivity of mictic female production, Mictic females similarly appeared both in the 3rd generation of groups A (high density was maintained during the 1st and the 2nd generation) and B (high density was maintained only during the 2nd generation). No mictic female was seen in group C which was treated only by low density. There seems to be at least two stages in the process of bisexual reproduction. The 1st is to acquire the ability to produce mictic female, which is naturally prepared as parthenogenetic generation goes on. The 2nd step is the action of an external factor like high density, which is effective only for animals which have passed through the 1st step.
Successive culture to the 25th generation of 20 strains showed that a strain acquired the ability generally in an early generation. Then it became intense with the progress of generations. The frequency of mictic female production differed with strain. Therefore it will be possible to select a suitable one for masscultur or artificial induction of dormant egg formation.