Introduction. It is well known that the yellow-fever mosquito, Aedes Aegypti (Stegomyia fasciata), being a domestic species, having a fairly long life in adult stage, and exhibiting the custom of hiding itself in most ingenious ways, is particularly subject to carriage for long distances on vessels, railroad trains, in baggage, etc. It is assumed that in this way it was carried from America to Africa, or vice versa. Through such transportation agencies this mosquito is distributed over great distances, and during the warm seasons it may be carried far beyond areas where it is capable of maintaining itself permanently. It has been presumed also that when carried during the warm seasons to colder climates, it is annually exterminated by the cold, after breeding for a certain number of generations, and, consequently, the permanent distribution is limited in a general way, apparently by the frost line.