1968] 
Robinson — Behavior of Pterinoxylus 
203 
in press a ) , it is reasonable to assume that adaptations will occur 
which serve to conceal these features. Many stick mimicking phas- 
mids appose the anterior limbs and protract these in line with the 
long axis of the body. This can be regarded as both concealing limb 
structure and increasing the apparent length of the body and its 
resemblance to a tapering stick. In phasmids the protracted limbs 
enclose the antennae and partially enclose the head, and thus may 
be regarded as also concealing these features of insect structure. A 
similar and convergent anterior limb attitude is adopted by some 
stick mimicking mantids and ploiariids, although in these cases the 
antennae and head are not concealed. 
However, most of the phasmids which adopt a stick attitude at 
rest stand with the intermediate and posterior legs extended in at- 
titudes similar to those involved in locomotion. The conspicuousness 
of these legs may be reduced by cryptic coloration and the possession 
of complex foliaceous processes but they could still be cues which 
would enable a sophisticated predator to detect the presence of the 
insect. This view is supported by my work (Robinson, in prep.) with 
Rufous-naped Tamarins, Saguinus geoffroyi. These small insectivorous 
primates proved capable of detecting the presence of dead phasmids 
which had only the intermediate or posterior legs extended, much 
more rapidly than those which had been arranged in the cataleptic 
stick position (see below) in which all the legs were concealed. 
These experiments were conducted with a phasmid Metriotes diodes 
Westw., which drops from the resting substrate when disturbed and 
assumes a cataleptic stick attitude after dropping. This attitude in- 
volves anterior limb protraction and the apposition of the other limbs 
to the sides of the body. Similar attitudes are assumed in similar cir- 
cumstances by other phasmids (see Steiniger 1933) and also by 
phasmids which rest with the body closely appressed to the substrate 
(Robinson, in press 3 -). The resting attitude of P. spinulosus can 
perhaps be regarded as the functional homologue of such attitudes 
in so far as it involves concealment of the intermediate and posterior 
limbs. The P. spinulosus resting attitude effects leg concealment 
whilst permitting a sticklike orientation to the substrate and without 
impairing the efficiency of the legs as locomotory organs. 
Consideration of the presumed startle display also raises a number 
of questions. The bases for assuming that the display has an anti- 
predator function are its form and the circumstances in which it 
occurs. In the male it has similar elements to the startle displays of 
mantids (Crane 1952, Varley 1939) involving sudden apparent in- 
crease in size and the revelation of previously concealed bright colors. 
