1. Experiments have shown that ether, nitrous oxide, and carbon dioxide all have significant and different post-anaesthesial physiological effects on workers of Myrmica. They reduce longevity and all except nitrous oxide reduce oviposition.

2. Nitrous oxide causes abnormally early accumulation of an egg mass.

3. The effects of these three anaesthetics can be distinguished from one another, and from the effects of nitrogen anaesthesia (presumed anoxia). Their effects may occur together with, and in addition to, those attributable to anoxia.

4. The effects of the anaesthetics on Myrmica longevity appear to be due to the direct physiological action of the anaesthetic and do not operate indirectly via ethological change as supposed in previous work on Apis.

5. These results are discussed in relation to previous work including the concept of artificial ageing which is shown to be untenable in this instance.

Formerly Carnegie Research Student, Glasgow University.