1963 ] Eisner , Hurst and Meinwald — Defense Mechanisms 
97 
fig. 2). Each consists of a racemose cluster of secretory cells (A), 
drained by numerous fine cuticular ductules that converge to merge 
into a single long and slender efferent tube (B). The tube leads to 
a capacious and strongly muscled storage reservoir (C), from which 
secretion is expelled via a short ejaculatory duct (D) that opens on 
the hypopygium. 
The opening itself is slit-like, the duct at this point being main- 
tained closed under the spring-like action of an especially modified 
cuticular valve. Examination of a KOH-treated specimen consisting 
of cuticle alone confirmed the fact that closure of the orifice is 
maintained passively without muscle enforcement: the orifice was 
tightly collapsed, and could only be opened by prying with a glass 
needle. 
The ejaculatory duct is surrounded by circular muscles (Plate 11, 
fig. 4, C), but these do not extend the full length of the duct. The 
terminal portion is naked (E), and consists of only the cuticular 
intima and its surrounding epithelium. It is evidently this naked 
section that is extruded at the moment of discharge to form the spray 
nozzle. Two special muscles seem to effect nozzle extrusion. One 
of these is a broad and short sheet of fibers (A), originating on the 
hypopygial cuticle near the pore, and extending obliquely to the duct 
to merge with the duct’s intrinsic circular muscles. Contraction of 
this muscle pulls on the duct, forcing its evagination. The second 
muscle (B) inserts on a cuticular flap at the edge of the pore and, 
after bending around the duct, extends to attach on the hypopygial 
cuticle. This particular muscle serves to force apart the cuticular 
valve that ordinarily closes the pore, thus enabling the nozzle to be 
extruded at the time of discharge. Without a gaping pore orifice, 
extrusion would be impossible and the tube would simply buckle. 
b. A bacion 
In this millipede, as in so many others that produce defensive 
secretions, the glands are distributed segmentally, one pair to each 
of most diplosegments. Only the first postcephalic segments and a 
few preanal ones lack glands. The openings of the glands are tiny 
pores situated dorsolaterally on the anterior half of the diplosegment, 
each on an elongate crest that protrudes from the tergum (Plate 9, 
fig. 2; Plate 12, fig. 3). 
The ease with which a given A bacion may be induced to discharge 
varies greatly. Some discharge at once, the moment they are first 
picked up, but this is the exception. More often they will tolerate 
considerable prodding and even prolonged handling before the dis- 
