864 mr. kbxmqs authaitdaIiI OEH hie [Dec. 4, 



cannot be in all cases a sexual attraction, for it is exhibited by 

 larvae and even by eggs 1 ; neither can its object always be to 

 attract prey : that it is a warning to enemies seems hardly pro- 

 bable, for most small animals, whether aquatic or terrestrial, are 

 attracted rather than repelled by light. In the bacteria and 

 in forms like Noctiluca it appears to be an adventitious result of 

 metabolism rather than to bring any practical gain to the organism ; 

 among the adults of the Lampyridce it very probably acts as a sexual 

 charm ; among the larvae of the same group its purpose may possibly 

 be to attract prey. In the case of the aquatic form there must be 

 some reason why the larvae should come to the surface at night and 

 display their light on the top of the water. That purpose can hardly 

 be to wain surface enemies not to eat them, or to scare away aerial 

 aggressors. Much more probably the light attracts some surface or 

 aerial prey. The fact that the light disappears when the water is 

 disturbed also supports this view. It is not to the advantage of 

 the larvae to attract the attention of any animal big enough to make 

 a commotion in the pool. 



In three other species of Lampyrid larvae, all terrestrial, — two, 

 which were both over an inch in length, being found crawling on 

 the ground among bushes in Patalung, and the other seated on a 

 cocoanut-husk under a house in Kelantan — the light, which was 

 situated in all cases on the ventral surface of the abdomen, was 

 steady, and neither flickered as it did in the winged forms, nor 

 slowly disappeared without apparent cause as in the case of the 

 aquatic larva. A small specimen which I found under the mosque 

 at Aring, mistaking it at first sight for luminous fungus which grew 

 there commonly, continued shining when picked from the ground, 

 but immediately became dark when dropped into formol, and never 

 shone again. Professor Poulton tells me that North-American 1 

 fire-flies lose control of their lights when placed in a cyanide-bottle, 

 and are no longer able to extinguish them. The same is true of 

 the Malayan winged forms, though occasionally a specimen becomes 

 entirely dark for a few minutes when first introduced into the bottle. 

 The aquatic larva which allowed its light to reappear after it had 

 been in corrosive sublimate for some minutes was probably only 

 just beginning to become affected, for corrosive penetrates hard 

 chitin very slowly. The insect allowed itself, when once affected, 

 to be transferred into a more pungent medium before it finally 

 ceased to shine. 



Of all the manifestations of luminescence among animals there is 

 none more curious, or, in the present state of our knowledge, more 

 inexplicable, than the manner in which large numbers of individuals 

 of certain fire-flies are able to display their light with absolute 

 apparent simultaneity and unison and with regular intervals of 

 darkness, under circumstances which make it impossible for all the 

 members of the swarm to see one another. Even the power, 



1 See Dubois. Bull. Soc. Zool. France, xii. 1887, p. 137. 



2 Darwin makes very much the same remark with regard to the Brazilian 

 Forms, in his ' Voyage of a Naturalist ' (p. 30,). 



