ABSTRACT
A novel experimental technique incorporating a double-chambered array, which allows the independent and reversible exposure of head and tail ends of the insect to the surrounding atmosphere, without otherwise altering the constraints on the insect, is described.
Using this technique, it has been possible to demonstrate that rapid uptake of water from subsaturated atmospheres occurs in Thermobia only when the tail-end is exposed.
This effect is immediately and completely reversed when the tail-end is shielded from the atmosphere, and can be restored again on re-exposure of the tail-end, as shown repeatedly during electrobalance recordings.
The relative humidity within the closed head-end chamber slowly rises, but within the closed tail-end chamber it falls, to approximately 50 % (the critical equilibrium humidity) with the desiccated insects and to 60-65% with hydrated insects, whilst the anal valves show movements indicating the operation of the rectal uptake mechanism.
These findings are compatible with the anus being the avenue for the passage of water into the insect from the atmosphere.
