204 



ANIMAL LUMINOUSNESS. 



tion of an imponderable agent by the nervous 

 systems of the animals, just as the electrical 

 fishes give their shock without the interposition 

 of any visible or ponderable secretion. In this 

 view we may regard the luminous organs as 

 playing the same part in relation to the evo- 

 lution of light as the electrical organs of the 

 torpedo do to the production of the shock. 

 The single fact of luminousuess continuing in 

 the organs or in their effused fluids, after they 

 have been removed from the body of the ani- 

 mal, seems to point to a great difference ex- 

 isting between the two classes of phenomena 

 which we have just compared, in certain ani- 

 mals; but it may be that the difference is 

 more apparent than real ; for this fact may be 

 explained by supposing that a phosphoric sub- 

 stance really does enter into the composition 

 of the light-giving organs; and yet we may 

 with great probability conjecture that it is not 

 the chief agent in causing the phenomena of 

 luminousness. It remains, then, for future in- 

 quirers to determine the chemical composition 

 of the luminous organs, and the fluids emitted 

 by the animals, the phenomena of whose lu- 

 minousness seem to be irreconcileable with the 

 idea of their being dependent on the nature 

 of these fluids ; if they be found to contain 

 phosphoric matter, it may be concluded that, 

 as this does not appear to be essential in them 

 to the production of the phenomena of lu- 

 minousness, so neither may it be in other ani- 

 mals, in which it is believed to be the chief 

 agent in the manifestation of their light-giving 

 function. 



To this theory, (which is only a combination 

 of the two most generally received in modern 

 times,) we do not, in the facts which have 

 come under our notice, see any serious objec- 

 tion. The only argument adduced against 

 Macartney's theory by Tiedemann and other 

 physiologists, who have carefully considered 

 the facts of the case, is founded on the circum- 

 stance of the light continuing, in a certain 

 degree, for some time after the death of the 

 animals, which, of course, cannot be supposed 

 to be owing to the continued operations of the 

 nervous system. This posthumous light, how- 

 ever, may depend on the phosphorescence of 

 the luminous organs or their effused fluids in 

 virtue of their composition, while the full evo- 

 lution of light during life may be produced 

 chiefly by the play of imponderable agents in 

 and from the nervous system, independently, 

 in some cases, of the chemistry of the fluids ; 

 in other cases, aided and modified by the nature 

 of these and by the structure of peculiar organs. 



It is scarcely necessary to take particular 

 notice of the various other theories that have 

 been suggested, as the facts stated in the pre- 

 ceding part of the article are sufficient to set 

 them aside. 



VIII. Uses of animal luminousness. We 

 know nothing certainly with regard to the 

 uses of the light-giving function ; but as almost 

 all observers have remarked that male insects 

 seem to be attracted towards their mates by the 

 brilliancy of the light emitted by the latter, it 



has been generally supposed that the luminous- 

 ness is subservient to the generative function. 

 Although it may be so to a certain extent, it is 

 obviously not essentially connected %vith it, 

 even in the glow-worm; tor the light endures 

 long after the season of love is past. Some 

 have conjectured that the light may sometimes 

 be the means of preserving its possessors from 

 the destructive attacks of enemies. Thus Shep- 

 pard observed a large beetle running round a 

 shining scolopendra, as if wishing to attack it, 

 but seeming to be scared by the light. We 

 may imagine, also, that the light enables its 

 possessors to see surrounding objects at night, 

 and so to thread their way in safety through the 

 darkest places. 



Considering that, in the ocean, there is abso- 

 lute darkness at the depth of 800 or 1000 feet, 

 at least that, at such depths, the light of the 

 sun ceases to be transmitted, Macculloch has 

 suggested* that, in marine animals, their lumi- 

 nousness may be " a substitute for the light of 

 the sun," and may be the means of enabling 

 them to discover one another, as well as their 

 prey. He remarks, " It seems to be particu- 

 cularly brilliant in those inferior animals which, 

 from their astonishing powers of reproduction, 

 and from a state of feeling apparently little 

 superior to that of vegetables, appear to have 

 been in a great measure created for the supply 

 and food of the more perfect kinds." 



IX. Luminousness of animals not innate, 

 and other allied phenomena. We have ac- 

 counts of the surface of the human body ap- 

 pearing luminous in consequence of phos- 

 phoric matter being largely mixed with the 

 sweat in the course of various diseases. The 

 urine also both of men and several of the 

 lower animals is occasionally luminous under 

 similar circumstances. It is said that the urine 

 of Viverra mephitis and V. putorius is al- 

 ways so.f 



The eyes of human albinoes, almost all the 

 mammalia which possess a tapetum lucidum, 

 as also those of some birds of prey, serpents, 

 and insects, seem to shine in a feeble light 

 from the reflexion and concentration of the 

 rays falling upon them from external objects. 

 Pallas thought that this light was developed in 

 the retina, and regarded it as an electrical phe- 

 nomenon. But it has been plainly proved by 

 Prevost, Gruithuisen, and Esser,J that the 

 shining of the eye depends, in most cases, on 

 reflexion of light. They found that there was 

 no appearance of luminousness in absolute 

 darkness; and that the eyes of dead animals 

 gave the same effect as those of the living, 

 when placed in similar circumstances. 



It would appear, however, from some obser- 

 vations made by Rengger on the eyes of a 

 certain South American ape, ( Nyc tipithecus 

 trivirgatus,) that there is reason to believe in 



* Edin. Encycl. art. " Phosphorescence." 



t Langsdorff, Reise. ii. 184. 



j Edin. New Phil. Jour. ii. 164. 



<j See also Hessenstein, de Luce ex quorundam 

 animal, oculis prodeunte, atque de Tapeto lucido. 

 Jenae, 1836. 



