During meiosis I, the #78# chromosomes in a diploid cell line up at the equator of the cell. Note that the chromosomes have already replicated.
#39# chromosomes will then move to each pole of the cell. The difference between anaphase in meiosis I and mitosis is that in meiosis I, the centromere does not split, so the sister chromatids are still held together.
The result is #39# chromosomes at the poles of the cell. The chromosome number is reduced from #2n# (diploid) to #n# (haploid). Then the cell will undergo meiosis II, where the cell will divide, producing #4# haploid daughter cells with half the number of chromosomes of the parent cell.
