LUMINOSITY OP MARINE ANIMALS AND INSECTS. 329 



396. But the Noctilucae and Acalephae are by no means the 

 only luminous animals which tenant the deep. Many Zoo- 

 phytes appear to have this property in an inferior degree, and 

 also some of the Echinodermata. Of the lowest class of 

 Mollusks, the Tunicata, a very large proportion are luminous, 

 especially those which float freely through the ocean, and 

 which abound in the Mediterranean and tropical seas ; the 

 brilliancy of some of these can scarcely be surpassed. Among 

 some of the Conchifera, also, the phenomenon has been ob- 

 served ; as well as in certain marine Annelida. Other marine 

 animals of higher classes are possessed of similar properties ; 

 thus, many Crustacea, especially the minuter species, are 

 known to emit light in brilliant jets ; and the same may be 

 said of a few Fishes : but it is probable that the luminosity 

 attributed to many of the latter is due to the disturbance they 

 make in the surrounding water, which excites its phospho- 

 rescence in the manner just explained. In all these, the 

 general phenomena are analogous, the luminous matter ap- 

 pearing to be a secretion from the surface of the animals, and 

 to undergo a sort of slow combustion by combination with 

 oxygen. Wherever it is presented by these animals, it is 

 always most brilliant upon the surfaces concerned in respira- 

 tion. The light continues for some days after death ; but 

 ceases at the commencement of putrefaction. 1 



397. In the class of INSECTS, there are several species which 

 have considerable luminous power ; and in these the emission 

 of light is for the most part confined to a small part of the 

 surface of the body, from which it issues with great brilliancy. 

 The luminous Insects are most numerous among the Beetle 

 tribe, and are nearly restricted to two families, the Elateridas, 

 and the Lampyridce. The former contains about 30 luminous 

 species, which are known as fire-flies; these are all natives of 

 the warmer parts of the New World. Their light proceeds 

 from two minute but brilliant points, which are situated one 

 on each side of the front of the thorax ; and from another 



1 There are certain cases, however, in which the production of Light, 

 like that of Electricity ( 423), appears to be a peculiar manifestation 

 of Nervous power. There is strong reason to believe that Nerve-force 

 may be directly metamorphosed (as it were) into these or other forms of 

 physical and vital force, according to the principle of " Correlation * r 

 now generally admitted as regards the Physical Forces. 



