Retrogression of the ovaries of Xenopus laevis occurs if toads are kept for long periods in an insufficient volume of water. Atrophy takes place in spite of regular feeding and change of water and occurs more frequently and to a greater extent than in toads which are underfed. Overcrowding is followed by a diminution in food intake; the weekly consumption of food being halved in the case of females subjected to the maximum population density. Under natural conditions the seasonal decrease in

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... er volume of the ponds in which Xenopus lives may induce or at least contribute to the maintenance of the retrogressive phase of ovarian activity which normally occurs.