Almost any collection of water will serve as a nursery for the larvæ, unless indeed, there be a decidedly strong current; but the situations taken by preference during the breeding season are small stagnant pools and domestic collections of water, such as small tanks, broken crockery, empty tins, &c.; while wintering larvæ prefer the larger ponds and marshes which are permanent throughout the cold weather, and especially select those in which there is sufficient vegetation, reaching to the surface of the water, to afford cover and protection from their numerous enemies. Practically speaking, wintering larvæ will never be found in tanks or ponds devoid of fairly robust vegetation, and it may easily be understood from this fact that the clearing away of reeds, grasses, and weeds of all sorts during the cold weather from all such collections of water which may be found near an inhabited site is a most important sanitary measure. Some species prefer the fairly clean water of marshes and ponds, while others luxuriate in the dilute sewage of the domestic waste water, but it would occupy too much space to go into any detail on this subject, and all that the sanitary amateur need remember in this connection, is that any and every collection of water, capable of standing for ten days or a fortnight, should be regarded as dangerous to health in any country where malaria is known to exist. For our purposes, it will suffice for the reader to understand the general characteristics of three sorts of mosquitoes. First, there are the common _Culex_ mosquitoes, which are, almost everywhere, far more common than the others. They are usually of a dull grey colour, and with very few exceptions, their wings are quite plain and free from spots. As will be seen from the photographs in the accompanying plate, they sit in rather a humped-up position, and the proboscis is obviously much thinner than the body, its appendages, or palps, being held apart from it. Mosquitoes of this sort cannot convey human malaria, though they are instrumental in conveying a similar disease for certain animals. They are to be found, in greater or less numbers, throughout the year. The second sort is the _Stegomyia_, which is the genus concerned in the conveyance of yellow fever. These mosquitoes are seldom to be seen except during the rains, and rest in much the same position as the _Culices_, which they resemble closely in form. Their wings are never spotted, and almost all are small insects clothed with jetty-black scales, picked out with an ornamentation of dazzling white lines on the body and spots on the abdomen and legs. [Illustration: _PLATE II._ Photographs of living mosquitoes. Above, ♂ and ♀ _Culex_ mosquitoes in profile; in the middle, ventral aspects of the same; and beneath, ♀ and ♂ _Anopheles_ mosquitoes. About twice natural size.]