operate on the luminous matter (while in the living body,) only indirectly, by exciting the animal.-The luminous matter, in all situations, so far from possessing phosphoric properties, is incombustible, and loses the quality of emitting light, by being dried, or much heated.—The exhibition of light, however long it may be continued, causes no diminution of the bulk of the luminous matter. It does not require the of pure air, and is not extinguished by other gasses.

presence

The luminous appearance of living animals is not exhausted by long continuance, or frequent repetitions, nor accumulated by exposure to natural light; it is therefore, not dependent upon any foreign source, but inheres as a property, in a peculiarly organized animal substance or fluid, and is regulated by the same laws which govern all the other functions of living beings.

The light of the sea is always produced by living animals, and most frequently by the presence of the medusa scintillans. When great numbers of this species approach the surface, they sometimes coalesce together, and cause that snowy or milky appearance of the sea, which is so alarming to navigators. These animals, when congregated on the surface of the water, can produce a flash of light, somewhat like an electric corruscation. When the luminous medusæ are very numerous, as frequently happens in confined bays, they form a considerable portion of the mass of the sea, at which times they render the water heavier, and more nauseous to the taste; it is therefore adviseable to always strain sea water before it is drunk.

The luminous property does not appear to have any connection with the oeconomy of the animals that possess it,

except in the flying insects, which by that means discover each of sexual congress. purpose

other at night, for the

EXPLANATION OF THE FIGUres.

Fig. 1. The cancer fulgens, discovered by the Right Hon. Sir JOSEPH BANKS, of the natural size.

Fig. 2. The same animal magnified.

Fig. 3. The medusa pellucens, also found by Sir JOSEPH BANKS, represented of the natural magnitude.

Fig. 4. The limulus noctilucus, discovered by Captain HORSBURGH, Considerably enlarged.

Fig. 5. The luminous medusa, discovered by me, which I conceive to be the medusa hemispherica: it is shewn of the largest size I met with.

Fig. 6. The central process of this animal's body magnified, in order to explain its structure. The thick tentacula in which it terminates are seen covered with small cups or suckers.

Fig. 7. The beroe fulgens, discovered by me, shewn in its most elongated or relaxed form, which it assumes commonly when swimming quickly.

Fig. 8. The same animal in the most contracted form.

Fig. 9. The minute species of medusa, discovered by me, which is the most frequent cause of the luminous appearance of the sea, represented of the natural size.

Fig. 10. The same animal magnified, exhibiting a puckered or tucked-in appearance on one side.

Fig 11. Is the animalcule discovered by FORSTER, of the natural size.

Fig. 12. The same, greatly magnified, to shew the intes

tinal parts. Both these figures are copied from the original drawings, in the possession of the Right Hon. Sir JOSEPH BANKS.

Fig. 13. Is an enlarged view of the inferior surface of the abdomen of the lampyris lucida, after the integument had been removed. a a a represent the three masses of luminous substance which are applied to the three last rings of the abdomen. bbb the arrangement of cellular or interstitial substance on the other abdominal rings, which gives the pale colour to the whole belly of this insect.

Fig. 14. Represents the common glow-worm, with the posterior portion of the back cut away to expose the sacs of huminous matter in situ on the last ring of the belly. a indicates the sac of one side; the intestine is seen to lie between them.

Fig. 15 and 16. Are the sacs of the glow-worm prodigiously magnified to shew their structure. Fig. 16 is cut open to expose the luminous matter it contains: the coat of the sac is still seen to preserve its figure.

Fig. 17. Is the elater noctilucus, with the shell of the corcelet removed on one side, by which the organ of light is uncovered. a the yellow transparent spot of the corcelet. b'the oval mass of luminous substance surrounded by an irradiation of the interstitial substance. c the ends of the muscles which were on the inside of the corcelet.

Fig. 18. Is the posterior angle of the corcelet of the elater noctilucus magnified. a the radiated appearance which the interstitial substance has round the oval mass of luminous matter. This mass is seen to consist of a number of smaller parts. b shews the appearance of the interstitial substance,