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CHAPTEE IX. 



On the Distribution of the Culicidae. 



The Culicidce are a truly cosmopolitan family, and may 

 be found everywhere from the tropics to well within the 

 polar circle. Their commonness indeed depends rather on 

 the state of civilisation of a region than upon its geographi- 

 cal position. In new countries, in regions where the 

 severity of the climate is such that they cannot support a 

 sufficient population to undertake the complete drainage of 

 the area, and amongst people whose civilisation, however 

 old, has not reached the stage of "tidiness" and order, 

 gnats and Mosquitoes will be found to be numerous and 

 troublesome. As examples of this may be mentioned the 

 cases of Lapland and the north-western portions of British 

 America, where, during the short summer, they constitute 

 a veritable pest ; so that, in the former country, the 

 nomadic inhabitants are obliged to frequently change their 

 grazing grounds to enable themselves and their herds to 

 escape from their insect tormentors ; while in Manitoba, 

 it is not uncommon for horses and cattle to be "stampeded" 

 from the unbearable pertinacity of the indigenous species. 

 In tropical countries again, the commonness of Mosquitoes 

 is due far more to the difficulties of securing efficient 

 surface drainage, and to the careless domestic habits of the 

 people, than to any special favourableness of the climate. 

 On the other hand, in countries such as England, Northern 

 France and Germany, where centuries of human inhabita- 

 tion have perfected drainage, and domestic neatness has 

 reached almost to the position of a religious duty, gnats 

 are so rare that, when they appear in any numbers, they 

 are commonly suspected of being a recent importation. 



Even in Holland, where the nature of the country 

 appears to be entirely in their favour, they are by no 



