JURA. LUMINOUS ANIMALS. 199 



pearing alternately, and probably, in consequence of the 

 will of the animal. That it is the result of the will, 

 is indeed almost proved, since it can be produced by 

 noises which are capable of exciting alarm without dis- 

 turbing the water. The same is to be observed in the 

 larger fishes. Thus if a noise be made by striking on 

 the gunwale of a boat when a shoal of pilchards is under 

 it, the whole will in an instant become luminous, exhibit- 

 ing the splendid appearance of a continuous sheet of 

 light; momentary, but renewable on repeating the same 

 alarming sound. It is impossible at present to ascertain 

 the means by which this effect is produced. That it is 

 not the result solely of their impulse against luminous 

 matter existing in the water, whether dead or living, is 

 certain ; since the same effect cannot always be produced 

 at those times by other agitation. Possibly the luminous 

 matter may exist in the mucous secretion of the slyn, 

 and thus be capable of excitation by the mere effort of 

 violent motion and consequent impulse on the water, in 

 cases where this matter does not exist in the sea in a 

 detached state. No explanation has yet been given of 

 the power by which the luminous land animals obscure 

 their light ; yet in them it is equally known to be under 

 the direction of the will, and also to be connected with 

 essential purposes in their economy . The property of emit- 

 ting light has been indeed supposed to be more common 

 among those than among the marine tribes, and it has been 

 found to exist in the genera Elater, Lampyris, Fulgora, 

 Scolopendra, Pausus, Limulus ? Galathea, Lynceus. The 

 slender enumeration of the marine animals already given, 

 is sufficient to prove that it is possessed by a much greater 

 number even of species among the inhabitants of ocean ; 

 and the superiority of the several races themselves is 

 numerically such, that while, in a few climates, the twinkle 

 of an insect is occasionally seen, the nocturnal darkness of 

 the immense ocean is illuminated by its inhabitants. In 

 the insect tribe, it has been supposed to serve only for a 



