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Psyche 
[September 
are in the forward position and before the conspicuous backward 
stroke, there is a period during which the wings appear to be moved 
against the raised tegmina in a series of short duration, low ampli- 
tude thrusts. The extent of movement during these thrusts is so 
slight as to be barely measurable from film analysis. During display, 
the membranous area of the wing is not flat but quite clearly curved 
downwards at the margins so that the wing is convex above and 
concave below. 
Ruud, quoted by Rehn (1957) described the stridulation as being 
a noise not unlike that of “a bumble bee or distant airplane”. Sounds 
are extraordinarily difficult to describe in words and it therefore 
seems useful to include portions of a sonogram of this stridulation 
(Figure 4). This represents the first and last 2.4 seconds out of a 
stridulatory bout of over fifteen seconds. The stridulation proves 
to be an untuned noise without discernable harmonics and with in- 
termittent variations in intensity. The periods of intense noise vary 
in duration and interval, waning in the former respect towards the 
end of the display. Both direct observation and analysis of film 
suggest that the intense sound production, reflected by the dense 
portions of the sonogram, may occur when the wings are in the 
forward position described above. The relatively quiet period would 
then correspond to the periods of backward wing movement when the 
tegmina are being lowered. This hypothesis could be checked by 
making a film of the wing movements with a precisely synchronized 
sound track. 
As in the case of the male display, that of the female may be fol- 
lowed by the assumption of a bizarre position similar to that shown 
in Figure 2 (with the exception of the wings which are folded and 
concealed). With successive stimulation the tendency to display 
decreases. Males eventually fly off whilst females walk rapidly 
away from the disturbance, giving sporadic displays whilst walking. 
Discussion 
Consideration of stick mimicry in general and that of phasmids 
in particular, raises a number of interesting problems. Most insects 
which are regarded as stick mimics possess morphological features 
which are incongruous with detailed resemblance to sticks but are 
necessary for essential biological activities. The walking legs of 
phasmids are obvious examples. If visually hunting insectivorous 
predators use typical features of insect organization as cues in prey 
detection (a possibility which I have developed elsewhere, Robinson, 
