io8 
Psyche 
[June 
noticeable injury, they nevertheless desisted instantly from further as- 
sail and fled. Chlaenius is evidently endowed with a mechanical as well 
as a chemical weapon, and the former might be of particular impor- 
tance at times when the beetle’s secretion is temporarily exhausted. 
2. Versus Abacion. 
Three millipedes (3-5 cm. in length) were released individually 
near the entrance of a Pogonomyrmex nest, at a time when the ants 
were highly active and aggressive, as evidenced by the readiness with 
which they attacked and overcame mealworms (larvae of Tenebrio 
molitor) introduced as occasional controls. The millipedes walked 
amidst the swarming ants, and dozens of casual encounters between 
ants and millipedes were seen to take place, but in not a single 
instance did an ant attempt to bite or sting a millipede, nor did a 
millipede ever discharge. The reason for this was the remarkable 
fact that A bacion responded instantly to contact with an ant by coming 
to an abrupt halt, and remaining motionless thereafter until the ant 
departed or, more usually, until seconds after the ant’s departure. 
While “death-feigning” in this fashion, the millipede evidently fails 
to evoke a full-fledged aggressive response from the ants. Time and 
again a millipede was released near the nest entrance, but it eventually 
always made its way to the safe outskirts of the nest, pausing inter- 
mittently during its escape whenever single ants or groups of ants 
scurried over its body, but never once being induced to discharge. 
When an ant contacted the millipede’s head, and also apparently when 
the glandless postcephalic segments were touched, the millipede came 
to a halt with its front end coiled beneath the body, a response 
already noticed when the animals were stimulated by hand (see lb 
above). Otherwise, when contact was with the body itself, the 
millipede simply halted without altering its stance. 
In order to test for the actual repellency of the secretion, millipedes 
were first subjected to artificial traumatic stimuli locally applied, and 
then released with the ants. Under these circumstances, the ants never 
even contacted the millipede, but turned around and retreated as soon 
as they came to within close range. As was the case with Chlaenius , 
the millipedes remained repellent for considerable periods after a dis- 
charge. Invulnerability of several minutes was the rule, even when no 
more than a few adjacent glands had been activated [the vapor 
pressure of />-cresol, as estimated by extrapolation from values given 
in the International Critical Tables (1928), is as low as that of 
772 -cresol, i.e. ca. O.i mm at 25 °C]. 
Abacion is slower in its locomotion than Chlaenius. Six specimens 
