Cells collected from the morula, the developmental stage prior to the blastocyst. The morula, a solid ball of about 16-30 cells, seems able to sustain the loss of a few cells without developmental damage so that the remaining cells can continue to develop. Cell extraction from the morula is already being used in some clinics to screen for for genetic disorders in embryos produced by in vitro fertilization. Researchers have recently shown that cells isolated from a mouse morula can give rise to embryonic stem cells while the remaining morula cells develop into a healthy mouse. However, this process may still be morally objectionable to some because of the chance of harm to the morula, and because the long-term effects of removing cells from a morula are not yet known.