THE VICTORIAN NATURALIST. 89 



while the similar office is performed by birds, bats, and dragon- 

 flies in catching and devouring the winged adults. The wide 

 distribution of many species over the earth's surface is due almost 

 entirely to man's agency, either by water in ships as in the 

 Hawaiian Islands, or by trains as in the case of many newly- 

 opened inland centres. 



The chief Australian forms are three species of Anopheles 

 in Queensland and the Blue Mountains, N.S.W., one species 

 of Megarhinus, a form with a curved proboscis, of which 

 practically nothing is known as to its life -history ; and in 

 Victoria, Stegomyia fasciata, a spotted form with banded legs, 

 which serves as the carrier of yellow fever elsewhere, and 

 Gulex frenchii and C. occidentalis ; also four species of purely 

 vegetarian genera. 



Malaria is carried from infected to healthy human individuals by 

 Anopheles (chiefly A. maculipennis) after an interval of 7 to 8 

 days, which period is necessary for the development of the sexual 

 phase in the wall of the gnat's stomach, and the formation and 

 transport of the spores to the salivary glands, whence they are 

 poured into the blood with the " poison." 



Yellow fever is probably due to some protozoan parasite 

 following a somewhat similar life-round to that of the malarial 

 organism. The germ of yellow fever is carried by Stegomyia 

 fasciata after a period of 10-13 ^^J^ after its ingestion from an 

 infected individual. Because this mosquito is found in Victoria 

 it does not follow that there is any special danger of yellow fever, 

 unless one or more cases of this disease were introduced and 

 exposed in such a way as to allow the mosquitos to become 

 infected by sucking the blood, and to then fly away to some healthy 

 individual. 



The Oriental tropical disease, filariasis, which is due to the 

 presence of parasitic worms of the genus Filaria under the skin, is 

 propagated by Culexfatigans, and possibly some other species, in 

 which the embryos must pass part of their existence. It is 

 considered probable that other diseases are also carried by 

 mosquitos — e.g., cholera, plague, Mediterranean fever, and 

 typhoid. 



Remedial work against the early stages of the life-history of 

 mosquitos may be carried out by the treatment of breeding 

 places with insecticiiies, such as kerosene poured on the surface of 

 the pools once in seventeen days, or three weeks, the abolition 

 of breeding places by filling with earth or drainage of swamps, 

 or by the introduction of fish, frogs, «&c. Screening of houses, 

 smoking-out of rooms, and such measures, seem the only means 

 of getting rid of the adults. The value of eucalyptus trees in 

 driving away the adults, while great in some parts, is very doubt- 

 ful in others. 



