Synkaryon

The active pronucleus of each pair moves across the protoplasm and fuses with the opposite passive pronucleus, and thus two synkarya are formed. Each synkaryon divides into four, and thus each cell contains at this period eight nuclei which form the nuclei of eight spores, protected within the thick cyst-wall.

Persistence of two functional synkarya appears to be a clear recapitulation of the ancestral temporary conjugation, when two exconjugants developed. In the second type (Fig. 47, b), this recapitulation is not so strong. Here, although each conjugant produces two pronuclei and two synkarya are formed in the synconjugant, one of them soon degenerates, only the other remaining functional, dividing, and giving rise to new macronuclei and micronuclei of the synconjugant.

The next step is a fusion of the stationary nucleus with the newly invaded migratory nucleus in each cell. Thus, synkarya are formed by mutual fertilization.

One gamete nucleus from each gamont migrates across a cytoplasmic bridge into the other cell and fuses with the nucleus which did not migrate, so that synkarya are formed in each cell.