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要旨

Ether-induced avoidance of the center of an arena by a walking fly does not seem to be the outcome of at least two post-narcotic effects of ether vapor: the inactivation of acetylcholinesterase (Gage et al. 1979), and the inactivation of locomotion (van Dijken et al. 1977). The latter is actually due to a change in the action pattern of search and search control. The centrophobism arising either irreversibly in response to ether treatment, or reversibly in the course of accommodation to a new territory, increases the probability of brief stops at the outer boundary of the arena (Figs. 2–4).
Acquisition and maintenance of ‘orientedness’ by exploration of the available territory or evaluation of sensory aids to orientation appears indispensible if a fly wants to avoid the center of the arena. However, centrophobism can be explained without assumption of voluntary behavior. Persistence of direction during random walk in the arena is sufficient to divert locomotor activity from the center to the surround (Figs. 5, 6). The centrophobism found, so far, is equivalent to a ‘mean free path’ of about 4 cm in etherized flies, and about 2 cm in non-etherized flies (Table 1). Search control by variation of persistence in the track of a fly is compatible with results obtained in other insects.