Psyche 
[June 
114 
is produced by some cockroaches (Chadha et al., 1961a; Roth et al., 
1956) and certain Hemiptera (Blum, 1961; Waterhouse et al., 
1961). 
It is also not uncommon for relatively closely related forms to pro- 
duce very different secretions. Millipedes and carabid beetles do in 
themselves illustrate this point. Among the millipedes, non-phenolic 
compounds that have been identified include hydrogen cyanide, ben- 
zaldehyde (Eisner, H. E., et al., 1962), and />-benzoquinones (re- 
viewed in Roth and Eisner, 1962). Of the three carabid genera other 
than Chaenius that have been studied, one ( Calosoma ) produces 
a phenolic compound (salicylaldehyde ; Eisner et ah, 1962), but the 
other two do not: Pseudophonus secretes formic acid (Schildknecht 
and Weis, 1961); Brachinus sprays />-benzoquinones (Schildknecht, 
1957 ) . 
These chemical similarities on the one hand, and dissimilarities on 
the other, illustrate some striking convergent and divergent trends 
in the evolution of arthropod secretions — trends that will some day 
have to be given the proper explanation they deserve. But this will 
have to await an understanding of the particular biochemical path- 
ways by which the secretions are synthesized, and of the special rela- 
tionships of these pathways to the fundamental biosynthetic machinery 
of the cell. 
Summary 
1. The carabid beetle Chlaenius cordicollis Kirby, and the chor- 
deumoid millipede Abacion magnum (Loomis), produce defensive 
secretions which have been shown by infrared spectrophotometry and 
vapor phase chromatography to contain ra-cresol ( Chlaenius ) and 
/>-cresol ( Abacion ) 
2. Chlaenius has two glands that open near the tip of the abdomen. 
It discharges its secretion as a spray, ejected from either one gland or 
from both, depending on whether the causative traumatic stimulus is 
unilaterally or bilaterally applied. The spray is not directed at ran- 
dom, but through bending of the abdominal tip is aimed with some 
accuracy toward the body region traumatized. 
Abacion has a pair of glands per each of most diplosegments. The 
discharge is a liquid ooze, proceeding normally from only those glands 
close to the stimulus. 
3. A brief account is given of the structure of the glands, as well 
as of their inferred mode of operation. 
4. Experiments are described in which individual Chlaenius and 
Abacion were exposed to attacks by ants and several vertebrates. 
