The objectives of this article as I saw them were, (1) to show how fetal gonads acquire the ability to function as endocrine organs, and (2), to show the mechanisms by which the endocrine secretions modulate male development. The researchers went through an extremely extensive explanation of the formation of the sexual phenotypes by detailing the development of germ cells. They explained how women's and men's gonads appear identical until Leydig cells, which synthesize testosterone, appear in the connective tissue. This is when differentiation begins. The mechanism that this differentiation occurs is as follows. There are two duct systems which are basically sex specific. In men, Wolffian ducts are dominant and Mullerian ducts are regressive. Whereas in women it is just the opposite. Jost believed that the fetal testis secret a hormone which causes such a differentiation. In order to confirm this belief, he removed the gonads from embryos, prior to the onset of phenotypic differentiation. All resulted in female phenotypes. The male phenotype is induced and will not manifest if the proper secretions are not made from the testis. Although the article fails to mention how, "Jost deduced that two secretions from the fetal testis are essential for male development - Mullerian-inhibiting substance and androgen." The mechanism in which spermatogenic tubules form Mullerian-inhibiting substance is still unclear to scientists. Problems with improper levels of this hormone result in genetic and phenotypic reproductive disorders. The other hormone secreted by the testis is testosterone. It has two functions; it promotes maturation of the spermatogenic tubules (and is therefore indirectly effecting the levels of Mullerian-inhibiting substance), and it has its well known essential role in the development of the male genital tract. Throughout this article there were several areas where it seemed to me, issues were unresolved, however seemed to me that we have the technology to resolve them. For instance "The Character of the acceptor sites within the nucleus (that is, whether protein or DNA) and their number are not resolved." Couldn't one do a radioactive trace or a non-vital stain of some sort to distinguish the protein from the DNA. The development of one's sex is therefore far more than just a genetic decision, it is (once again) a complex cascade of hormones acting on receptors. These receptors go on to activate effector molecules which activate target molecules. If at any point this system is disrupted in any way, one either has the underdevelopment or incorrect development of the phenotypical gonadal characteristics.