Figure 1. Definition of the optimal male age for spermatid collection.

a) Representative photomicrograph of a cell suspension prepared from the testis of a male mouse at 24 days of age. Arrows indicate round spermatids, which are easily identified by a round nucleus and a high cytoplasmic/nuclear ratio. b) The proportion of round spermatids among testicular cells from 18 days to 24 days after birth. The percentages of round spermatids in testicular suspension increased consistently from days 18 to 24 (P<0.05 between groups). The cells were counted in two different males by two different operators. The horizontal bars indicate the average.