Meiosis of primary spermatocytes and early spermiogenesis in the resultant spermatids in newt, Cynops pyrrhogaster in vitro.

Dissociated spermatogenic cells were cultivated within the collagen matrix at low cell density. The largest cell type in the culture was identified as the primary spermatocytes by their size and the morphological characteristics revealed by ultra-thin sections. Chromosome analysis showed that about 90% of the cells examined were either in first or second meiosis. Within the collagen matrix, the fates of 282 single primary spermatocytes at meiotic stage in diakinesis or metaphase were followed. In a few days, most of them gave rise to four spermatids, passing through first and second meiotic divisions. About 80% of the spermatids formed motile flagella. They grew about 20-60 micrometers a day. The final state of the differentiation attained in our culture conditions was the spermatids with localized spherical nuclei and motile flagella, about 500 micrometers in length after 1-month's culture. Ultra-thin sections of the spermatids show that the rings, neck-pieces, and acrosomes developed in the cells.