Survival of spermatozoa in the reproductive tract of the bitch was studied by examination of the female genitalia at measured intervals after copulation. Motile spermatozoa were found in the lumen of the uterus in undiminished concentrations for 4 to 6 days after copulation; numbers progressively declined but motile spermatozoa were observed as late as 268 hr after copulation. Clusters of spermatozoa were observed in a high percentage of the uterine glands. The disappearance of spermatozoa was associated with the onset of metoestrus, not with time in the uterus. Bitches bred late in oestrus and examined in metroestrus had few spermatozoa compared with bitches examined in oestrus at a comparable time after copulation. Large numbers of spermatozoa were never found in the oviducts or ovarian bursae; they were consistently found here between 20 and 40 hr after copulation, a single observation showed spermatozoa in the oviducts at 168 hours. Tubal ova were recovered from eight bitches in metoestrus, in five cleavage had begun; tubal ova were recovered from four bitches in oestrus, none had undergone cleavage. Examination of the ovaries indicated that ovulation most commonly occurred within 48 hr after the onset of oestrus.
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