M. boulengeri is oviparous; males are in breeding condition in spring. H, peronii is viviparous; males are in breeding condition in autumn and winter. The former has abdominal fat bodies; the latter does not. The amounts of fat in tails, fat bodies, eggs, and the rest of the body were measured at different times of the year in both species. Changes in these fat stores suggest that fat from tails and, where present, fat bodies, is used by females for producing eggs and by males for activities associated with reproductive activity. In both sexes of both species there were large differences between individuals in the amount of stored fat. Removing tails from females made them produce fewer eggs; the reduction was greater in H, peronii. When M. boulengeri were fasting, they used more fat from their tails than from any other source, but they used up a higher proportion of fat body fat than of their other fat stores.