Thus we can see that, while the old theory of Kirby and Spence had some facts to support it, the one now in vogue is purely fanciful. Until some better suggestion is made, it would perhaps be as well to consider the luminous organ as having "no very close and direct relation to present habits of life." About their present habits, however, especially their crepuscular habits, there is yet much to learn. One thing I have observed in them has always seemed very strange to me. Occasionally an individual insect is seen shining with a very large and steady light, or with a light which very gradually decreases and increases in power, and at such times it is less active than at others, remaining for long intervals motionless on the leaves, or moving with a very slow flight. In South America a firefly displaying this abnormal splendour is said to be dying, and it is easy to imagine how such a notion originated. The belief is, however, erroneous, for sometimes, on very rare occasions, all the insects in one place are simultaneously affected in the same way, and at such times they mass themselves together in myriads, as if for migration, or for some other great purpose. Mr. Bigg-Wither, in South Brazil, and D'Albertis, in New Guinea, noticed these firefly gatherings; I also once had the rare good fortune to witness a phenomenon of the kind on a very grand scale. Riding on the pampas one dark evening an hour after sunset, and passing from high ground overgrown with giant thistles to a low plain covered with long grass, bordering a stream of water, I found it all ablaze with myriads of fireflies. I noticed that all the insects gave out an exceptionally large, brilliant light, which shone almost steadily. The long grass was thickly studded with them, while they literally swarmed in the air, all moving up the valley with a singularly slow and languid flight. When I galloped down into this river of phosphorescent fire, my horse plunged and snorted with alarm. I succeeded at length in quieting him, and then rode slowly through, compelled to keep my mouth and eyes closed, so thickly did the insects rain on to my face. The air was laden with the sickening phosphorous smell they emit, but when I had once got free of the broad fiery zone, stretching away on either hand for miles along the moist valley, I stood still and gazed back for some time on a scene the most wonderful and enchanting I have ever witnessed. The fascinating and confusing effect which the appearance of fire at night has on animals is a most interesting subject; and although it is not probable that anything very fresh remains to be said about it, I am tempted to add here the results of my own experience.