The effect of post-ovulatory ageing of mammalian eggs before mating or insemination has been extensively studied, and the variable though relatively short fertilizable life of the egg has been documented for a considerable number of species (for review see Blandau, 1961). It is not clear, however, to what extent the fertilizable life is an intrinsic property of the egg or is under the influence of the conditions prevailing in the Fallopian tubes. Nor is it clear whether the abnormalities associated with ageing eggs, such as polyspermy, spontaneous activation, fragmentation and loss of fertilizability, are to some degree determined by the nature of the tubal secretions.
In the short interval during which post-ovulatory ageing occurs, the secretions of the Fallopian tube are subjected to the influence of ovarian progesterone rather than to that of oestrogen which predominated at the normal time of mating and ovulation. Two recent experiments in the