Under this head, it is our intention to consider the circumstances under which light, electricity and caloric, are generated in the animal system. The subject is exceedingly interesting, and it has been enriched by numerous observations, the united efforts of the naturalist and chemist. Still, however, there prevails a considerable diversity of opinion, respecting the manner in which these substances are produced, or the share which the vital principle contributes towards their developement. As these bodies frequently appear to be produced contemporaneously, in the changes to which matter is subjected, they are to be viewed in this chapter in connection, in expectation that the mode of production of one, may help to illustrate the origin of antoher.

LUMINOUSNESS OF ANIMALS.

The faculty of emitting light does not appear to be possessed by any individuals of the classes Mammalia, Birds or Reptiles, Several fishes, however, exhibit this remarkable property; particularly the Dorado, Mullet, Herring and Sprat. The Spams chrysurus, an inhabitant of the seas of Brazil, is said to be luminous in such a remark able manner, that when a few individuals are swimming in company, they emit so much light, that in & dark night a person might see to read by its aid. But considerable suspicions may be entertained on this subject, whether the light is emitted by the bodies of fish, or by the number of minute parasitical animals which adhere to the surface of the skin.