Psyche 
[June 
1 1 6 
(text-fig. 2) and prevents the contents from interacting, must be 
virtually leak proof. Lack of output under these conditions also 
demonstrates that casual contact with other millipedes, such as oc- 
curred almost continuously during confinement in the chamber, does 
not constitute an appropriate stimulus for the discharge. 
Cyanogenesis in animals is rare, and so far as known is restricted 
to polydesmoid millipedes and certain moths (Jones et al., 1962). 
But among plants it is widespread, and occurs in several hundred spe- 
cies of diverse families (Seifert, 1955). The mechanism in plants 
may also be defensive, since as a rule the liberation of hydrogen 
cyanide is initiated only in response to injury. Cyanogenetic capacity 
of plants has been measured, and found to vary over a broad range. 
Mean output in Apheloria and Pseudopoly desmus is below the upper 
range of values recorded from plants (Table 1). However, this com- 
parison is of only limited significance. The values for plants are 
usually obtained by measuring the cyanide released after complete 
trituration of whole plants or parts thereof. Actual amounts liberated 
spontaneously by a plant for defensive purposes — as, for instance, 
when an insect bites into one of its leaves — has never been measured. 
The technique described here may be sufficiently sensitive to be em- 
ployed for this purpose. 
Summary 
1. A simple photometric assay for hydrogen cyanide is described, 
sensitive to 0.6 fig. 
2. The assay was used to measure the cyanogenetic output of the 
defensive glands of two species of polydesmoid millipedes, Apheloria 
corrugata and Pseudopolydesmus serratus. 
3. Output is highly variable in both species. Mean yield is 114 fig 
HCN in Apheloria , and 41 fig HCN in Pseudo poly desmus. Recorded 
maxima for each species are, respectively, 645 and 81 fig HCN. 
4. The assay should prove useful for measuring cyanogenesis in 
other organisms, including plants. 
References cited 
Davenport, D., D. M. Wooton and J. E. Cushing. 
1952. The biology of the Sierra luminous millipede, Luminodesmus 
sequoiae Loomis and Davenport. Biol. Bull. 102: 100-110. 
Deniges, G. 
1895. Sur une nouvelle methode cyanimerique et sur les applications 
qui en derivent. Ann. Chim. Phys. 7th ser. 6: 381-428. 
