1. Experiments are described which show that the rate of water-loss from living and dead worker bees is increased when a variety of dusts are brought into intimate contact with the surface of the cuticle. The common property of the more effective dusts is their capacity to act as adsorbents. Considerable evidence has been accumulated to suggest that the dusts need not abrade the surface of the cuticle in order to effect an increased water-loss and that the dusts act by adsorbing the epicuticular lipoid.

2. The surface relief of the cuticle of the worker honey-bee is described and the importance of considering this feature of the insect in any experiments dealing with the action of dusts is demonstrated.

3. An evaluation of the physical properties of the epicuticular lipoid has indicated that it contains, or possibly entirely consists of, a hard wax similar to beeswax.

4. The action of the dusts and of chloroform suggests the absence of a continuous cement layer, and it is suggested that the wax approaches a monolayer in thickness, at least on some areas of the cuticle.

5. Living worker bees were shown to be capable of recovering their impermeability after dusting.

6. The type of waterproofing mechanism described in the honey-bee is not thought to be peculiar to that species. It is probably present in other Aculeates.

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