October 5, 1900.] 



SCIENCE. 



519 



animals killed by exposure to the sun do 

 not stain the alcohol as described above, 

 the repugnatorial fluid having oozed out 

 and been evaporated from the surface of the 

 segments. This suggests a further possi- 

 bility that the material elaborated in the 

 repugnatorial glands may not attain its 

 final and effective composition until di- 

 rectly or indirectly acted upon by the air. 

 Camphor would furnish a somewhat differ- 

 ent and probably more difficult problem, for 

 though not actively poisonous to us, its 

 fumes seem to have a very detrimental 

 effect upon many of the tracheate Ar- 

 thropoda. That some of the predaceous in- 

 sects might be active enemies of such an 

 animal as Polyzonium is entirely possible, 

 but it is also to be considered that the small 

 as well as the large Diplopoda may owe to 

 their repugnatorial secretions their com- 

 parative immunity from mites and other 

 parasites which commonly attack animals 

 of similar habits. The larger forms are not 

 entirely immune from mites, but when these 

 are found they seem always to be confined 

 to the immediate neighborhood of the head, 

 never occurring on the poriferous segments. 

 This susceptibility to injury from expo- 

 sure to sunlight may prove to be an expla- 

 nation of the hitherto not obvious utility of 

 the eyes of the Diplopoda, which are more 

 sensitive spots, probably quite incapable of 

 effective vision, though possibly of service 

 in seeking shelter. Perhaps some causal 

 relation may also be found in the fact that 

 in the large order Merocheta, where Prussic 

 acid is secreted, eyes are entirely wanting, 

 though absent only in a few subterranean 

 species of other groups. This absence of 

 eyes also renders apparently meaningless 

 the fact recorded by Bruner and Kenyon,* 



*Brnner, Insect Life, 1891, III., 319, describes a 

 yellow spot near the lateral edge of each cariDEe as 

 luminous. Kenyon, Fublications of the Nebraska 

 Academy of Science, 1893, 16, doubts whether the 

 luminosity belongs to the repugnatorial secretion be- 



that the repugnatorial secretion of a Ne- 

 braska species is luminous. From the sex- 

 ual standpoint the odor might have a func- 

 tion though the light were merely incidental, 

 but when the nocturnal habits of the ani- 

 mals are considered, phosphorescence may 

 be looked upon as affording a protection 

 additional to that of the odor of the re- 

 pugnatorial liquid. 



In the preceding discussion there has 

 been no intention to imply that the repug- 

 natorial secretion of Spirobolus is the same 

 as that of Spirostreptus, though there seems 

 to be greater similarity than with Polydes- 

 miis. Moreover the milky and particularly 

 malodorous liquid excreted by Spirostrephon 

 lactarium and probably by other members of 

 the family Lysiopetalidse is also obviously 

 different from any of the others, so that the 

 elaboration by the class Diplopoda of at 

 least four repugnatorial compounds seems 

 certain, and the idea that Prussic acid is 

 manufactured by all the pore-bearing Di- 

 plopoda is shown to be a quite unwarranted 

 generalization. 



Two other substances of similar quality 

 and function may be of interest in this con- 

 nection. One is to be found in the material 

 forcibly ejected by the so-called ' nasuti ' caste 

 or soldiers of termites of the genus Ptyotermes. 

 There are several such species in Liberia, 

 the largest, P. liberieiisis, being deeper brown 

 than the others and having the soldiers of 

 such size that the jets of liquid can by care- 

 ful observation be seen by the naked eye. 

 The fluid, which is secreted in a special ce- 

 phalic gland, is clear and watery and does 

 not stain the hands, though alcohol in which 

 the insects are collected becemes dark 

 brown. A smarting sensation in the eyes 

 cause it is described as confined to stationary spots. 

 But in a state of rest it could be expected that only 

 small quantities of the repugnatorial fluid would be 

 continuously given off, and evaporation would take 

 place in the cavity of the pore. Kenyon calls the species- 

 Foniaria luminosa, but a study of his specimens shows 

 that the generic afSnity is rather remote. 



