About the habits of Pyrophorus, the large tropical firefly which has the seat of its luminosity on the upper surface of the thorax, nothing definite appears to be known; but it has been said that this instinct is altogether nocturnal. The Pyrophorus is only found in the sub-tropical portion of the Argentine country, and I have never met with it. With the widely-separated Cratomorphus, and the tortoise-shaped Aspisoma, which emit the light from the abdomen, I am familiar; one species of Cratomorphus--a long slender insect with yellow wing-cases marked with two parallel black lines--is "the firefly" known to every one and excessively abundant in the southern countries of La Plata. This insect is strictly diurnal in its habits--as much so, in fact, as diurnal butterflies. They are seen flying about, wooing their mates, and feeding on composite and umbelliferous flowers at all hours of the day, and are as active as wasps during the full glare of noon. Birds do not feed on them, owing to the disagreeable odour, resembling that of phosphorus, they emit, and probably because they are to be uneatable; but their insect enemies are not so squeamish, and devour them readily, just as they also do the blister-fly, which one would imagine a morsel fitted to disagree with any stomach. One of their enemies is the Monedula wasp; another, a fly, of the rapacious Asilidas family; and this fly is also a wasp in appearance, having a purple body and bright red wings, like a Pepris, and this mimetic resemblance doubtless serves it as a protection against birds. A majority of raptorial insects are, however, nocturnal, and from all these enemies that go about under cover of night, the firefly, as Kirby and Spence rightly conjectured, protects itself, or rather is involuntarily protected, by means of its frequent flashing light. We are thus forced to the conclusion that, while the common house fly and many other diurnal insects spend a considerable portion of the daylight in purely sportive exercises, the firefly, possessing in its light a protection from nocturnal enemies, puts off its pastimes until the evening; then, when its carnival of two or three hours' duration is over, retires also to rest, putting out its candle, and so exposing itself to the dangers which surround other diurnal species during the hours of darkness. I have spoken of the firefly's pastimes advisedly, for I have really never been able to detect it doing anything in the evening beyond flitting aimlessly about, like house flies in a room, hovering and revolving in company by the hour, apparently for amusement. Thus, the more closely we look at the facts, the more unsatisfactory does the explanation seem. That the firefly should have become possessed of so elaborate a machinery, producing incidentally such splendid results, merely as a protection against one set of enemies for a portion only of the period during which they are active, is altogether incredible.