ANIMAL LUMINOUSNESS. 



199 



spectators, yet there was not one on board who 

 did not feel some decree of them ; and all im- 

 puted them to the effect of the light proceeding 

 from the surface of the ocean. Mr. Henderson 

 remarks : " For my own part, the headach, &c. 

 which followed immediately my looking at the 

 water, was particularly severe, nor did it go off 

 until morning. The effects I experienced were 

 like those produced by smoking too much 

 tobacco."* 



There have been recorded some accounts of 

 very intense light produced over a great extent 

 of the ocean's surface by luminous animals, but 

 it does not appear that any other voyagers have 

 experienced physical effects from the light such 

 as are described by Mr. Henderson. The great 

 intensity with which it is occasionally produced 

 by marine animals, however, is well illustrated 

 by the descriptions that are given of the moral 

 emotions with which it inspires the beholders. 

 Witness, for instance, Mr. Bonnycastle's descrip- 

 tion of a scene which he met with in the Gulf 

 of St. Lawrence, (7th Sept. 1826.) While it 

 was very dark, a brilliant light, like that of the 

 Aurora, was seen to shoot suddenly from the sea, 

 in a particular quarter. It spread thence over 

 the whole surface of the water between the two 

 shores of the Gulf; and shortly there was pre- 

 sented " one blazing sheet of awful and most 

 brilliant light." " Long tortuous lines of light 

 showed many large fishes darting about as if in 

 consternation at the scene." The light was suf- 

 ficient to enable one to see the most minute 

 objects on the ship's deck. On drawing up a 

 bucketful of the water, and stirring it with the 

 hand, it presented " one mass of light, not in 

 sparkles as usual, but in actual coruscations."f 



Messrs. Quoy and Gaimard state that in 

 handling luminous marine animals while alive, 

 they have always been sensible of an odour pro- 

 ceeding from them similar to that which is per- 

 ceived around a highly charged electrical appa- 

 ratus. 



The only observation with which we are ac- 

 quainted that seems to indicate the evolution of 

 heat in connexion with the light of animals, is 

 that reported by Macartney, who states that he 

 found the thermometer raised by two or three 

 degrees when placed in contact with a group of 

 living glow-worms shining, or even with their 

 light-giving sacs cut off. The repetition of this 

 experiment, however, has not produced the 

 same result in the hands of others : they saw no 

 rise of the thermometer. 



III. Circumstances in which light is given 

 out, and by which its intensity is affected. 

 It is not known whether there be any lumi- 

 nous animals that give out light in all circum- 

 stances, and at every period of their existence, 

 in their natural situations. So far as observa- 

 tion extends, certain mollusca, and some of the 

 species of elater appear to shine without inter- 

 mission. But most of the other light-giving 

 animals with which we are acquainted use their 

 peculiar function only occasionally, and that, 

 for the most part, under some kind of excite- 

 ment or irritation, natural or artificial. In the 



absence of more direct means of investigation, 

 we may, perhaps, attain to some measure of 

 acquaintance with the nature and analogies of 

 animal light by inquiring into those sources of 

 irritation under which it is given out. Here, 

 however, we are met by the difficulty of finding 

 contradictory statements of facts made by dif- 

 ferent observers. So that our exact knowledge 

 on the subject is still insufficient to admit 

 of any satisfactory conclusions being drawn. 

 What is known on this point may be conveni- 

 ently considered under the two following heads. 



I. Circumstances essentially connected with 

 the state of nature in which the animals are 

 placed when they give out, light. 



II. Circumstances artificially produced af- 

 fecting the emission of light. 



I. Natural circumstances in which light is 

 emitted by living animals. The luminousness 

 of animals in their natural state is affected by, 

 1. Changes in the state of the medium in 

 which they live, whether air or water, in regard 

 to its temperature and electricity. 2. By solar 

 light. 3. By abrupt collision with other bodies. 

 4. By loud noises. 5. By the internal move- 

 ments of the animals themselves, amongst 

 which may be included the exercise of the ani- 

 mal's will. 



1. Temperature, <c. By far the greater 

 number of luminous animals with which we 

 are acquainted are natives of warm climates ; 

 but those inhabiting the ocean are seen in 

 almost all latitudes, even in the coldest ; al- 

 though in these they are not so numerous, and 

 give less light. No aerial insects give out 

 light, in ordinary circumstances, excepting at a 

 temperature of about 50 Fahr. and upwards ; 

 and the higher the natural temperature, the 

 brighter is the light emitted. 



In temperate climates the Lampyrida shine 

 only in summer and autumn. L. noctiluca 

 appears in this country between June and Sep- 

 tember; L. splendidula, in Germany, is lumi- 

 nous in May ; and L. hemiptcru so early as in 

 the end of April. 



The light of pholas dactylus is strongest in 

 summer ; and that of marine animals in ge- 

 neral is increased before storms. 



2. Solar light. It is said that Scolopendra 

 does not shine at night excepting it has been 

 exposed during the day to solar light. A short 

 time of exposure to the sun's rays seems to be 

 sufficient to refresh its luminous power, as (like 

 all other light-giving animals) it secretes itself 

 as much as possible during the day. It is 

 stated by Btirmeister,* with regard to the Latn- 

 pyris Italica, that if it be kept some days in 

 the dark it entirely loses its luminousness, but 

 regains it on being again placed in the sunshine. 



3. Lunar light. Macartney remarked that 

 luminous medusa: generally retreat from the 

 surface of the water at moon-rise. 



4. Abrupt collision with other bodies. 

 Marine luminous animals very readily emi 

 their light on being struck by any moving body; 

 so that one of the most commonly observed 

 phenomena connected with this subject is the 



' Trans. Mcd. and Phys. Soc. of Calcutta, i. 107, 

 t Trans, of Lit. and Hist. Soc. of Quebec. 



* Manual of Entomology, transl. by Shuckbard, 

 p. 494. 



