DEFENSE MECHANISMS OF ARTHROPODS. XX. 
QUANTITATIVE ASSESSMENT OF HYDROGEN 
CYANIDE PRODUCTION IN TWO SPECIES OF 
MILLIPEDES 1 
By H. E. Eisner, D. W. Alsop, and T. Eisner 
Division of Biological Sciences, Cornell University 
Although much has been learned in recent years about the chemical 
nature of the defensive secretions of arthropods (for reviews see 
Jacobson, 1966; T. Eisner and Meinwald, 1966; Roth and T. 
Eisner, 1962; Schildknecht et al., 1964), virtually no precise mea- 
surements have been made of the quantities in which the active 
principles are produced and stored. In animals that discharge their 
secretion as a liquid, gland capacity may be estimated directly by 
weighing the amount of fluid ejected. But when the defensive sub- 
stance is emitted as a gas, a more refined assay is in order. In two 
previous papers of this series, we dealt with the production of gaseous 
hydrogen cyanide by certain species of millipedes, and described the 
structure and mode of operation of their cyanogenetic glandular appa- 
ratus (H. E. Eisner et al., 1963; T. Eisner et al., 1963). We have 
now developed a quick and highly sensitive assay for hydrogen 
cyanide, and it is our purpose here to report on the measurement of 
cyanogenesis in two species of millipedes, Apheloria corrugata and 
Pseudopoly desmus serratus (Text-fig. 1). Both are members of the 
order Polydesmida, the only one in which cyanogenetic species are 
known to occur. 
Polydesmoid millipedes generate hydrogen cyanide only in response 
to disturbance. The poison emanates as a gas from droplets of secre- 
tion discharged by special glands that open along the sides of the 
body. Apheloria and Pseudopolydesmus each have a total of 22 
glands, present in pairs on segments 5, 7, 9, 10, 12, 13, 15, 16, 17, 
18, and 19 (Text-fig. 2). In Apheloria , each gland is a two-com- 
partmented organ (Text-fig. 2). In the inner compartment (reser- 
voir) there is stored an aqueous emulsion of mandelonitrile, the 
adduct of benzaldehyde and hydrogen cyanide. The other compart- 
ment (vestibule) contains a catalyst, presumably an enzyme, that 
promotes the dissociation of mandelonitrile. The gland is constructed 
This study was supported by Grant AI-02908 from the National Insti- 
tutes of Health. We thank our colleagues, W. L. Brown, Jr., W. T. Keeton, 
J. Meinwald, D. S. Robson, and F. C. Steward, for helpful advice. The 
first three also read the manuscript. 
Manuscript received by the editor May 22, 1967 
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