LUMINOSITY OF MARINE ANIMALS AND INSECTS. 329 
_ 396. But the Noctiluce and Acalephe 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 Z’unicata, 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.? 
397. In the class of Iysxcts, 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 Elateride, 
and the Lampyride. The former contains about 30 luminous 
_ species, which are known as jire-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 
___? 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” 
now generally admitted as regards the Physical Forces. 
