The first oestrus and ovulation in the rat generally occur 24 hr. after vaginal opening. Prepuberal ovariectomy delays vaginal opening when performed between the 22nd and 40th day after birth and adrenalectomy in spayed rats delays it further (Wade & Haselwood, 1941). Although, according to Pfeiffer (1936), neonatal castration does not impede vaginal opening, information is desirable on the relationship between the age of vaginal opening and the presence of the ovary for variable periods of time after birth. Vaginal opening sometimes has been taken as the clearest index of the onset of puberty (Ramaley & Gorski, 1967), but this may not be true under experimental conditions, as is the case with the precocious vaginal opening observed following administration of testosterone propionate (Colombo, 1968).
The influence of the ovary during the prepuberal period on the maturation of the genital tract has been studied in Wistar rats. The experimental animals were
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