1963 ] Eisner, Hurst and Meinwald — Defense Mechanisms 1 13 
was to the sternite, there was in most cases no response at all, and in 
the few exceptions the reflex was delayed for at least two minutes. 
Evidently, when the cuticular barrier is a thick one, neither the secre- 
tions nor the pure phenols are very effective irritants. Moreover, none 
of the samples differed detectably in their activity. 
The possibility still remains that the lesser components are of more 
than incidental significance (they might, for instance, act as emulsion 
stabilizers) but the present data offer no basis for further speculation. 
V. Discussion 
The protective function of the glands seems established, certainly 
as regards ants. The special adaptive refinements of the discharge 
mechanism, such as Chlaenius ability to aim the spray, and Abacion s 
tendency to respond locally rather than from all glands at once, are 
by no means unique. Other carabids studied ( Brachinus , Calosoma) 
also aim their spray (Eisner, 1958a; Eisner et al., 1962). In fact, 
aiming appears to be the rule rather than the exception among arthro- 
pods that spray (Roth and Eisner, 1962). Similarly, other millipedes 
studied thus far, and including juoids, spiroboloids, spirostreptoids, 
polydesmoids, and polyzenoids (Kafatos 1961; Eisner, unpublished), 
all share with Abacion the habit of restricting their discharge to the 
region stimulated. 
The experiments with vertebrate predators were not nearly as con- 
clusive as those with ants. There was only one instance of clear-cut 
prey rejection, involving the collared lizard and Chlaenius, and it is 
significant that the beetle survived the encounter uninjured. With the 
jay, the evidence clearly points to the unpalatability of Chlaenius and 
Abacion, but the prey was always killed before being rejected. Con- 
tinued daily tests would have been desirable, since on the long run 
the bird might well have developed discriminatory tendencies. Similar 
long range experiments would have been justified with the grasshopper 
mouse, although with Chlaenius there is really no reason to anticipate 
eventual avoidance on the part of the mouse, since the beetle is sub- 
dued by a technique that evidently prevents effective employment of 
its weapon. 
It may seem surprising to find a beetle and a millipede — two 
arthropods of widely distant phyletic positions — producing nearly 
identical secretions, but this situation is not without precedent, p- 
Benzoquinones, for instance, are known from the secretions of certain 
millipedes, phalangids, and representatives of several insectan orders 
(for summary, see Roth and Eisner, 1962). The aldehyde 2-hexenal 
