In the perfect female glow-worm of this country, the light is emitted chiefly from the inferior and lateral surfaces of the two or three last segments of the abdomen. The male of the same species presents only two small luminous points on the sides of one of the segments. When the light-giving surfaces of the female lampyris nocaluca are narrowly examined, it may be seen that, on the penul timate and antepenultimate segments, they pre sent bands of a bright greenish-yellow light, which are abruptly terminated towards the trunk by an irregularly waved line ; and that from the rest of the same segments there issues a fainter light of a pale green colour. There is also a little light given out by the posterior extremity of the dorsal line. In L. italics, the two last segments are wholly and nearly equally luminous. Most of the glow-worms in displaying their light recurve their tails upon their backs, so as to bring their luminous surfaces into view.
noctilucus gives out light principally from two points of the thorax, which are some what raised, and of an oval shape; but it has also two light-giving organs situated beneath the wing-cases, which are not seen except when the insect is flying. Light is also emitted from the internal parts through the interstices between the abdominal segments.
In Impestris ocellata, the light is emitted from certain yellow spots upon the elytra : in scarabaus phosphoricus from the belly : in chiroscelis bilenestrata, (a New Holland insect) from two oval, hairy, reddish spots on its second ventral segment; while, in pauses spitz rococcus, a dim phosphoric light issues from its singular hollow globular antenna.
Macartney says that he always observed the shining of scolopendra electrica to be aecom panied by the appearance of an effusion of a luminous fluid upon the surface of the animal, paticularly about the head. On touching this, his finger and other bodies received on their surface a phosphoric light, which continued to shine for a few seconds, and then died away; and yet he could not see any actual moisture, even upon smooth glass, although examined immediately and attentively.
The researches of Treviranus have led him to conclude that there is no special luminous organ in insects; but that the generally dif fused fatty matter is the seat of the function, by which the luminousness is produced. Ile concludes, therefore, that, when the air has ree access to the interior of the body through the respiratory tubes, the whole of the internal organs give out light; and that this is not seen, excepting at certain points of the surface, merely because the integuments are not trans lucent.
V. Anatomy of light-giving organs.—The accounts of examinations of these organs that have hitherto been published are rather imper fect. This appears to be owing chiefly to the fact that the organs themselves are of very simple structure and furnish no materials for lengthened description. So much so are they
in insects, that one would be inclined readily to conclude with Treviranus, that they are nothing but the common fatty or interstitial substance which fills up the bodies of insects, slightly modified by the presence of some phosphoric matter, were it not for the fact, particularly observed by Macartney, that, in the glow-worm, the luciferous organs are ab sorbed after the season for their use is past, and their places supplied by the fatty sub stance. The following are the results obtained by this naturalist and by Spix from their dis sections of the glow-worm, the fire-fly, and the lantern-fly.
In the glow-worm, there is spread over the internal surface of the segments of the abdo men a yellowish substance of the consistence of paste, which is thickest in the middle of each segment, and terminates near each margin by a wavy outline. It is of a closer texture than the fatty matter, but otherwise resembles it. Besides this substance, the last segment is furnished internally, just beneath the most transparent part of its integument, with two small round bodies, lodged in depressions, which contain yellow matter of more close and homogeneous texture. Muller and Murray describe these round bodies as " two small ovate sacs, composed of thready membranes, and filled with a soft yellow pasty matter." Under the microscope, they appeared to Macaire to be composed of numerous branching fila ments, with minute granules adhering to them. It is from points of the surface corresponding to the situation of these round bodies that the light is most constantly and most brightly emitted. When dry, these luminous organs have somewhat of the appearance of gum. The dried matter is translucent and yellowish, becomes darker on being kept, and appears to be granular in its structure. Its specific gra vity is a little greater than that of water.
In the fire-fly, the internal concavities of the yellow spots of the corselet, whence the light proceeds, are filled with a soft yellow sub stance, oval in shape, and of very uniform consistence and density. This, under the mi croscope, appears to be formed of a large number of very minute parts or lobules, closely pressed together. Around these oval bodies, the fatty matter of the corselet is arranged in a radiated manner. Spix describes the same organs as " yellowish glandular masses, into which many branches of the trachea enter." In elater ignitus the masses of luminous sub stance are extremely irregular in their figure; they are situated close to the posterior angles of the corselet, and are more loose in their structure than the same parts in elator noctilucus.