The uterus and ovaries of 617 elephants shot in Zambia were examined. Corpora lutea seem to be necessary for the development of the endometrial glands, and before conception can occur, a certain critical mass of luteal tissue has to be achieved by accumulating crops of cl from successive oestrous cycles. The elephant can be either monovular or polyovular, and ovulation is spontaneous. New ovulations do not occur during pregnancy, and the presence of an embryo prolongs the life of the cl. There is great variability in luteal size, small cl being commonest in non-pregnant animals and large ones in pregnant animals. The cl do not enlarge during gestation, and some of the smaller ones may regress. The number of cl in pregnant elephants varied with the age of the cow, the younger elephants having a significantly higher number. Larger cl ( > 20 mm in diameter) predominated in older animals. Very little progesterone appears to be secreted by the corpora lutea, and the hormone could not be detected in the peripheral blood during gestation. If progesterone is necessary for pregnancy, the elephant must be extremely sensitive to it, and may be forced to accumulate a large mass of relatively inactive cl before sufficient hormone is available to enable the animal to become pregnant.
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