To living organisms producing offspring is the most fundamentally essential problem. The strategy of many organisms involves having males that continually produce sperm throughout their lifetime. On the other hand many aspects of the mechanism by which females produce eggs remain unclear. Dr. Shuhei Nakamura (researcher) and Associate Professor Minoru Tanaka in NIBB have discovered egg producing stem cells in the ovaries of adult female Medaka, and have shown that these stem cells continually produce eggs in the structure, germinal cradle, authors named. It is a well established theory that, within mammals, the propagation of egg producing stem cells terminates before birth. The results of this research have shown that egg producing stem cells exist in the ovaries of a vertebrate for the first time. In addition they solve the mystery of how fish can continually produce so many eggs. These results will be published in the journal gScienceh (Science Express) March 20th 2010.