102 
Psyche 
[December 
position of the mandibles. I am by no means certain that 
the inner faces ever actually come in contact with each other 
although it seems likely that such contact may follow the 
snapping together of the mandibles during an attack. When 
the mandibles are held in the position just described the 
apical teeth lie close together and parallel to each other with 
their tips extending beyond the inner border of the opposite 
mandible (Fig. 2). If one looks down the long axis of the 
closed mandibles the four apical teeth may be seen to enclose 
a diamond-shaped area whose size will depend upon the de- 
gree of closure of the mandibles (Fig. 3). The mandibles 
can be opened to an astonishing extent, their outer borders 
approaching the sides of the head under extreme conditions. 
As a rule, however, they are not opened so widely, their usual 
position during attack being approximately at right angles 
to the long axis of the head. Under such circumstances the 
trigger hairs may be readily seen (Fig. 4). These do not 
arise from the mandibles themselves, as is the case with 
other forms possessing similar gnathal apparatus, but are 
borne on two conical lobes which lie between the bases of the 
mandibles. The trigger hairs are about two-thirds as long 
as the mandibles, and, since they project forward, it may be 
readily seen that objects which they touch should lie within 
the arcs described by the closing jaws. Anyone familiar 
with the mandibular organization of Odontomachus or 
Anochetus will recognize the essential similarity of the struc- 
tures just described in Strumigenys. Since we know that 
Odontomachus is able to dismember other insects with its 
pincer-like mandibles it seems reasonable to expect analo- 
gous reactions in the case of Strumigenys. My observations 
have supported this expectation but it must be borne in mind 
that the exceedingly deliberate actions of Strumigenys result 
in a type of attack which appears very different from the 
energetic activities of Odontomachus. 
As soon as the colony had recovered from the shock of 
transplantation and seemed at home in its new surroundings 
I cast about for a suitable victim with which to test the idea 
just mentioned. The small size of the Strumigenys worker 
considerably limited the choice. I wished to have the victim 
a more active insect than the Strumigenys and prudence for- 
bade the use of any form which might possibly damage the 
