204 
Psyche 
[September 
In the females the increase in apparent size is not striking but here 
there is the significant additional factor of the acoustic component. 
The form of defensive adaptations in animals must clearly be a com- 
promise between the requirements of defense and those of other, and 
perhaps conflicting, biologically important activities. In Neotropical 
phasmids of several genera (representing several families) the ability 
to fly may be possessed by both sexes (e.g. Metriotes , Prisopus , 
Pseudophasma f I sag or as, Stratocles, etc.) or only males (e.g. Pteri- 
noxylus, Bacteria , etc.). Whatever the causes of the tendency to- 
wards flightlessness in females, we can ask whether there is a 
minimum size to which wings can be reduced and still be effective in 
startle displays. If there is, it is conceivable that some species may 
evolve towards a compromise between reducing organs no longer 
serving their primary function and the requirements of their sec- 
ondary function, and approach this level. Others may add an acoustic 
component to the display which may reduce the importance of its 
visual aspects and enable a reduction beyond the level of a purely 
visual display. 
The interpretation of the wing display and stridulation of the 
female P. spinulosus as a startle display is admittedly based on in- 
ferences and can only be ultimately resolved by well-designed experi- 
ments with predators. However, it is given in circumstances consistent 
with this interpretation and has not been observed in any other cir- 
cumstances. It is not given (so far as I can determine) by undis- 
turbed active females at night when it could conceivably occur as 
a means of attracting males (and enabling males to locate females), 
and did not occur prior to, during or after the two matings I ob- 
served. In these cases the males approached the females and assumed 
a copulatory position in the mannner I have described for the Ori- 
ental phasmid Orxines macklotti De Haan (Robinson 1964). Con- 
spicuous displays by winged phasmids for which an anti-predator 
function has been claimed (or can be inferred) have been described 
for seven species representing seven genera. All, with the exception 
of the female P. spinulosus display, involve vertical wing erection. 
Sound production occurs in the displays of Eury enema goliath (Gray) 
and Tropidoderus childrenii (Gray) according to Bedford and Chin- 
nick (1966). These authors attribute the sound production to the 
raising and lowering of the wings which accompanies movements 
of the anterior legs. Carpenter (1942) reports observations by E. 
Burtt on a similar display by a Palophus species from Tanganyika 
and Foucher (1916) reported sound production in Cyphocrania 
