On the responses to environmental stimuli, and the sensory physiology of Millipedes (Diplopoda).



    1. Department of Zoology, University of Cambridge: now at the Department of Zoology, King's College, University of London
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The behaviour and sensory physiology of Paradesmus gracilis (C. L. Koch) and Blaninlus guttulatus (Bose) have been investigated. Both species posses a dermal light sense, and respond to light stimuli by means of a simple orthokinesis. Their temperature reactions fall into three categories: a general orthokinetic metabolic effect upon speed of locomotion, duration of spiral reflex, etc., a preference shown klinokinetically for temperatures about 15°C.; and orthokinetic activity stimulated by sudden drops in temperature. The temperature sense cannot be aseribed to any particular sensillae, but resides in the antennae as well as elsewhere. Positive geotaxis become apparent under the influence of the orthokinesis engendered by desiceation. The Tömösvary organs may be gravity receptors, but if so the stimulation of various proprioceptive organs by the weight of the body acting on limtes is probably also concerned in the reception of the stimulus.

No orthokinetic response to humidity comparable with that found in woodlice and wireworms has been observed: the millipedes show maximum locomotory activity at all humidity ranges, but once they have finally come to rest, they do not readily start moving again. Responses to moisture, however, are far more important in their behaviour; they are purely orthokinetic, and probably a general effect of dehydration. Possibly both Tömösvary organs and trichoid sensillae register vibrations: the millipedes respond by curling up (spiral reflex), but very slight vibrations frequently stimulate locomotory activity. Reactions to contact stimuli are of very great significance in the behaviour of millipedes. They are chiefly orthokinetic, and the tactile hairs on the limbs, sides of the body, and particularly on the antennae are the sensory receptors.

Millipedes do not respond to odours, but there is an orthokinetic “attraction” to gluclose and sucrose with a threshold about 0·5 gm. litre. There is no attraction to asparagine and strach, but urea repels Blavials. Antennary and gnathochilarial basiconic sensillae are the receptors for contact chemical stimulation. Removal of, or painting over the antennae induces a state of depression which persists until death.

The significance of the behaviour and sensory responses of millipedes in relation to their ecology is discussed with particular reference to the importance of Blaniulus as an agricultural pest.