ANIMAL LUMINOUSNESS. 



201 



the glow-worm continue to shine in carbonic 

 acid gas. Immersion in oils of all kinds de- 

 stroys the light-giving properly in most of the 

 insects endowed with it; but in Lumpyris 

 italica, Carradori found that the light conti- 

 nued to be emitted when the luminous part 

 of the body was plunged into oil. 



3. Pressure of their bodies, It has been 

 observed that shortly after the death of the in- 

 sect, the light-giving organs of elater emit light 

 freely when the body is bruised, and in general 

 mechanical irritations of all kinds cause a cer- 

 tain degree of increase in the intensity of the 

 light given out. Some animals, as pennatula, 

 seem to emit their light rarely, excepting in 

 such circumstances. 



4. Removal of the luminous organs, and mu- 

 tilation of these and of other organs. The 

 luminous organs may be cut out from the 

 bodies of glow-worms and fire-flies without the 

 peculiar property of the organs being imme- 

 diately destroyed. The emission of light can 

 for some time be re-excited by slight me- 

 chanical irritations ; as by touching the organs 

 with the point of a pin. Those of the glow- 

 worm have been seen to shine for two or three 

 days after excision, when slightly moistened 

 with water, heated or electrified. In experi- 

 menting on the same insect, Todd found that 

 the light was extinguished within six minutes 

 after the head was cut ofT; as also when the 

 luminous rings were cut into, but was renew- 

 able by the application of heat. Sheppard 

 removed the luminous matter from a glow- 

 worm ; the wounds healed within two days, 

 and the body became again filled with new 

 light-giving substance.* 



5. Exposure to various degrees of heat and 

 moisture. Light-giving insects in general do 

 not shine at any temperature below that of 

 53 Fahr. Macaire took some glow-worms 

 that had been kept for some time at a tem- 

 perature of 50 Fahr., plunged them into water 

 at 5.0, and gradually raised the temperature. 

 Light was emitted for the first time at 77, 

 and increased in intensity until the water was 

 at 105. At this temperature the animals died, 

 but the light continued until the temperature 

 had reached 134 5, when it wholly disap- 

 peared. When glow-worms are thrown alive 

 into water heated to 110 and upwards, they 

 die instantly, but at the moment emit a brilliant 

 light. When they are exposed to an artificial 

 cold suddenly, they perish at any degree below 

 the freezing point of water ; but the light may 

 be partially restored by a temperature of 70, 

 although the animals shew no other sign of 

 vitality. When the insects are dried artificially, 

 the light is extinguished, but it may be restored 

 by their being again moistened. 



6. Immersion in vacua. When glow-worms 

 are placed in vacua, their light fades, but re- 

 appears on admission of air. 



7. Removaljrom all foreign sources of light. 

 If luminous insects be confined in a dark 

 place, they shine little in the early part of the 

 day, but long before night they begin to do so ; 



* Kirby and Spcnce's Entomology, ii. 426. 



although generally, in their native situations, 

 they do not emit light until the twilight. If 

 the confinement in a dark place be protracted, 

 they do not shine so brightly as after having 

 seen the sun during the day. 



IV. Seat of luminousness in different animals. 

 In most of the luminous animals that inhabit 

 the ocean, a great part of their surface seems 

 to bf endowed with the property of forming, 

 and pouring out, a mucous fluid, which contains 

 the luminous matter, and is frequently mis- 

 cible with water and other fluids. This some- 

 times so entirely covers the whole animal as 

 to cause it to emit light from every point of its 

 surface ; but more generally when the animal 

 is swimming, the light is seen to proceed only 

 from certain regions. Some of the medusa, 

 even of the largest size, emit light from a very 

 small point, particularly when the luminous 

 organ is placed in the central parts of the body. 

 When the light is vivid, it seems to be larger 

 than it really is, from the refracting power of 

 the gelatinous tissues through which it passes. 

 Occasionally the luminous point has not a 

 diameter equal to the l-200lh of that of the 

 animal itself. In cydippe pileus and Oceania 

 pileata of the Baltic, Ehrenberg finds that the 

 light issues solely from the vicinity of the 

 ovaries, and in Oceania hemispherica, from the 

 bases of the cirri. P kolas dactylus gives out 

 light most strongly from the internal surface 

 of its respiratory tubes. The luminous mucus 

 is sometimes poured out even by very small 

 animals in such quantity as to leave a lumi- 

 nous wake behind them, as in an instance 

 mentioned by Quoy and Gaimard. These ob- 

 servers saw such luminous lines formed in the 

 paths of certain extremely small creatures, so 

 transparent that their forms could not be dis- 

 tinctly made out. The positions of their bodies 

 were marked in the water by bright spots, 

 which were followed in their course by lumi- 

 nous wakes, at first about an inch in breadth, 

 but afterwards by the movements of the water 

 spread out to the breadth of two or three 

 inches. This luminous mucus is supposed to 

 be the seat also of the remarkable stinging 

 property possessed by many of the aca/epha. 

 It retains its luminousness in some instances 

 for a day or two after being emitted by the 

 animal, but loses it whenever putrefaction 

 commences. 



But although this luminous mucus be so ge- 

 nerally secreted and emitted by marine ani- 

 mals, it is evident that the light given out by 

 many of them has its seat in certain organs 

 more or less internal, whence it proceeds in 

 gleams and momentary flashes that seem to 

 depend only on the movements of some im- 

 ponderable agent. The exact position and re- 

 lations of these organs can seldom be satis- 

 factorily discovered, but in some crabs and mi- 

 nute crustaceous animals that emit light, it is 

 observed to proceed from the central organs of 

 the nervous system. In other Crustacea the 

 whole body seems to be full of light, which is 

 emitted, as at so many windows, through the 

 translucent membranes interposed between the 

 segments of the crust. Dr. Macculloch con- 



