1900.] INSECTS OF THE “‘SKEAT EXPED1TION.” 863 
pool that we discovered that the light proceeded from beetle larvie, 
which were clinging, dorsal surface downwards, to the floating 
fronds of a small eryptogam. The luminous points were blue in 
colour and very brilliant, though small. They did not flicker like 
the lights of the fire-flies which flitted in hundreds over the surface 
of the marsh, and when they were extinguished they died away 
gradually. In the pool they did not change their position, but 
they became sometimes brighter and sometimes less bright slowly, 
ovcasionally dying out entirely for no apparent: cause. When the 
larva was taken out of the water, its luminosity disappeared, and 
did not reappear until it had been restored to its habitual element 
for some minutes. The light of some specimens which were placed 
with water and weeds in a glass jar, and brought near a lamp after 
they had recovered from their capture sufficiently to shine again, 
went out. After a longer or shorter interval of rest near the 
lamp, on different trials, it reappeared again, Poking them witha 
twig sometimes caused them to shine more brightly, but more often 
to become entirely dark. If several individuals were in a bottle 
and one of them became brilliant from any cause, the others 
followed suit after a few seconds. A specimen which was put 
into corrosive solution ceased to be luminous, but after about a 
quarter of an hour became exceptionally bright. It was then 
transferred to a weak solution of formalin ; whereupon its light 
went out finally, taking several seconds to disappear. 
During the day I was unable to find any of the larve on the 
surface of the pool; but the captive specimens had deserted the 
floating weeds before morning, and were crawling slowly on the 
bottom of the jar. I did not see them feed, though the water in 
the jar was full of small animals of different sorts—Copepods, 
Protozoa, and water-mites. Nor, while I was watching them, did 
the larve ever come to the surface to take in air or to breathe. 
I can find no special respiratory organs in my specimens: when 
alive no part of the body was silvery in appearance under water. 
Remarks.—The question of luminosity is one even more 
enigmatical than that of the sounds produced by insects. It is a 
phenomenon which is manifested right down among the Protozoa, 
and even in the border-land between the two great kingdoms ; it 
reaches its highest development among some of the Lampyride. 
In the Westmann Isles I have seen a whole village accidentally 
lighted up by the action of putrefactive bacteria in cods’ heads 
hanging to dry on the walls of the gardens; and a dead shark upon 
the shore was visible on the darkest night from the same cause to 
the distance of half a mile. Noctiluca and other marine animals— 
celenterates, crustaceans, tunicates, &c.—produce even more 
astonishing luminescent effects. It is not apparent what is the 
object of this display among these forms; though possibly in the 
case of the Medusz it may serve as a lure for prey, as it appears 
to do among certain deep-sea fishes. Among the insects and 
Myriapoda the purpose of luminescence is also obscure’. It 
1 See Dubois, Bull. Soe. Zool. France, ‘‘ Les Elatérides lumineux ” (1886), &e, 
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