When we consider the insect's delicate organ, so admirably fitted for the purpose to which it is applied, it becomes difficult to believe that it could have been so perfected except in a condition of things utterly unlike the present. There must have been a time when mosquitoes found their proper nourishment, and when warm mammalian blood was as necessary to their existence as honey is to that of the bee, or insect food to the dragon-fly. This applies to many blood-sucking insects besides mosquitoes, and with special force to the tick tribes (Ixodes), which swarm throughout Central and South America; for in these degraded spiders the whole body has been manifestly modified to fit it for a parasitical life; while the habits of the insect during its blind, helpless, waiting existence on trees, and its sudden great development when it succeeds in attaching itself to an animal body, also point irresistibly to the same conclusion. In the sunny uplands they act (writes Captain Burton) like the mosquitoes of the hot, humid Beiramar. "The nuisance is general; it seems to be in the air; every blade of grass has its colony; clusters of hundreds adhere to the twigs; myriads are found in the bush clumps. Lean and flat when growing to the leaves, the tick catches man or beast brushing by, fattens rapidly, and, at the end-of a week's good living, drops off, _plena cruoris."_ When on trees, Belt says, they instinctively place themselves on the extreme tips of leaves and shoots, with their hind legs stretching out, each foot armed with two hooks or claws, with which to lay hold of any animal brushing by. During this wretched, incom-plete existence (from which, in most cases, it is never destined to emerge), its greatest length is about one-fourth of an inch; but where it fastens itself to an animal the abdomen increases to a globe as big as a medium-sized Barcelona nut. Being silvery-grey or white in colour, it becomes, when thus distended, very conspicuous on any dark surface. I have frequently seen black, smooth-haired dogs with their coats, turned into a perfect garden of these white spider-flowers or mushrooms. The white globe is leathery, and nothing can injure it; and the poor beast cannot rub, bite, or scratch it off, as it is anchored to his flesh by eight sets of hooks and a triangle of teeth.