1. Ability to take up water in response to dehydration and injection of posterior pituitary extract was measured in two genera of frogs, Heleioporus and Neobatrachus, that live in areas of varying aridity in south-west Australia.

2. Species of Neobatrachus from dry areas took up water more rapidly than those from less dry ones. No such correlation could be seen in the species of Heleioporus.

3. No differences could be seen in the ability of any of the animals to withstand desiccation.

4. These findings are discussed in relation to the animals' behaviour in its natural environment.

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