1963 ] Eisner , Hurst and Meinwald — Defense Mechanis?ns 
99 
tinct phenolic odor finally becomes noticeable. But even the least 
responsive individual will eventually discharge when the stimulus is 
a more traumatic one, as for instance when legs are persistently 
pinched with forceps, or when the body is touched with a hot needle. 
The secretion is not sprayed as in Chlaenius , but is discharged as 
discrete white droplets that ooze forth from the various glands and 
collect at the pore openings (Plate 12, fig. 2). The discharge is not 
from all glands at once, but is restricted to the glands of the region 
traumatized. Insufficient millipedes wsre available to study the 
precise pattern of discharge localization, or to determine in some 
detail the relative effectiveness of various types of traumatic stimuli. 
It seemed clear, however, that the first glands to discharge are those 
of the specific segments stimulated and that, with persistent stimula- 
tion at the same locus, the response tends to spread to adjacent seg- 
ments, but never to more than a few on both sides of the area 
stimulated. Stimulation of the head — which lacks glands — results 
in an instantaneous ventral curling of the front end of the animal, 
so that the head is brought in close proximity to the first gland-bearing 
segments, which under these circumstances are ones that discharge. 
Once a millipede has been caused to discharge at a particular locus, 
subsequent discharges at other loci may usually be induced rather 
readily (e.g. by scratching with a cold needle), without resorting to 
the rather strong trauma (e.g. persistent pinching of legs, cautery) 
that is ordinarily required to evoke a first discharge. In all preceding 
respects, Abacion bears close resemblance to other millipedes whose 
discharge mechanism has been studied in some detail (Kafatos, 1961). 
Each gland of Abacion consists of a spherical articular reservoir 
(Plate 12, figs. 3, 4), dorsolaterally situated in the posterior half of 
the diplosegment, and embedded within the thick multilayered somatic 
musculature. As evidenced from microscopic whole mounts of stained 
preparations, the wall of the reservoir consists of an outer glandular 
epithelium and an inner articular intima. There is no surrounding 
musculature: examination in polarized light — which ordinarily reveals 
even the most tenuous muscle fibers (Eisner, 1962) — served to con- 
firm their absence. 
EXPLANATION OF PLATE 9 
Fig. 1. Ventral view of abdominal tip of Chlaenius , showing the slit-like 
gland opening as it appears at rest (a), and the nozzle (b) that projects from 
the opening at the moment of discharge (the nozzle was drawn from memory 
after observing beetles spraying under a microscope ; its general proportions 
are probably accurate). 
Fig. 2. Left lateral view of two diplosegments of Abacion, showing gland 
openings, one of them labelled (p). 
