1967] Eisner , Alsop & Eisner — Defense Mechanisms 
1 13 
water as the standard 4 . The assay was accurate to ± 0.6 fig hydro- 
gen cyanide, as was determined by measuring the efficiency of recovery 
of known amounts of hydrogen cyanide, generated in the apparatus 
by reaction of sodium cyanide and acid. 
RESULTS AND CONCLUSIONS 
A total of 157 adult Apheloria were tested, comprising 80 females 
and: 77 males. Of Pseudopolydesmus, only 11 males and 6 females 
were assayed. The results, plotted as hydrogen cyanide produced 
against body weight of millipede, are presented separately for each 
species in Plate 16. 
Cyanogenetic yield is evidently a markedly variable parameter in 
both species. Apheloria, which is larger than Pseudopoly desmus, has 
a higher mean yield than the latter (114 ^g/animal in Apheloria; 
41 fig/ animal in P seudopoly desmus ) . Yet Pseudopoly desmus has 
more than twice the mean output per unit body weight than does 
Apheloria (280 fig/g in Pseudopoly desmus ; 135 fig/g in Apheloria ) . 
In Apheloria, females tend to outproduce males; since females are 
also larger than males (note in Plate 16 the almost disjunct size dis- 
tribution of the sexes) they probably have larger glands. Additional 
data might have shown the same to hold for Pseudopoly desmus. 
Both species have considerable toxic potential, certainly at their 
higher levels of output. For example, a single Apheloria, weighing 
one gram and having a near maximum yield of 600 fig of hydrogen 
cyanide, produces the equivalent of 18 times the Lethal Dose of a 
300 g pigeon, 6 times the LD of a 20 g mouse, 0.4 times the LD of 
a 25 g frog, and 0.01 times the LD of man (Flury and Zernik, 
4 The shunting of the gas stream from one trap to the next sometimes 
occurred slightly after, rather than before actual clearness had been achieved. 
As a result, individual traps could contain more cyanide (as ammonium 
cyanide, bound to the excess ammonia in the suspension) than the predictable 
amount that had solubilized the silver iodide. The pooled sample was 
therefore sometimes clear rather than turbid. This necessitated the addi- 
tion, before backtitration with sodium cyanide, of sufficient fresh suspension 
to bring about a reappearance of turbidity, thus insuring the conversion of 
all cyanide to silver ammonium cyanide. Such added suspension was tallied 
as part of the total in the final computation. 
Explanation of Plate 16 
Cyanogenetic yield of individual Apheloria (left) and Pseudopolydesmus 
(right), plotted against body weight (males, open circles; females, closed 
circles). In Apheloria, mean yield (horizontal bar of crosses) and mean 
body weight (vertical bar of crosses) differs significantly (p<0.01) in the 
two sexes. In Pseudopolydesmus , due to the relatively scant data, mean 
output and weight are given for the population as a whole (single cross). 
