LIFE HISTORY AND SEASONAL PREVALENCE 143 



force them into retirement on the opposite account ; so that 

 in such places, all correspondents tell me that they are 

 present, in greater or less numbers, throughout the year ; 

 though even with them, the degree of prevalence is a good 

 deal influenced by such climatic variations as occur. Thus 

 there exists for many species, what may be called a southern 

 limit of hybernation, to the north of which it is compelled 

 to retire into seclusion during the winter ; whereas, further 

 south, they are able to remain in activity to a greater or less 

 extent throughout the year. In the case of our local species 

 in India of Anopheles, this line lies somewhere about the 

 26th parallel of latitude, for while they were certainly still 

 hybernating in Agra, in the middle of February, I found 

 them numerous and fairly active some hundred miles further 

 south, at Hoshangabad, in the Central Provinces. It should, 

 however, be needless to remark that it is impossible to lay 

 down any rigid limits in a case of this sort, and that it must 

 needs vary from year to year with temporary variations of 

 the character of the seasons. 



Our knowledge of the seasonal prevalence of individual 

 species is very limited, and in any case, can only be stated 

 for areas of small extent, but it may be broadly stated that 

 in each locality it may be fairly predicated from an inspec- 

 tion of the annual weather reports, as while some are 

 tolerant of the greatest heat, others are confined to seasons 

 of abundant rainfall. Were we even much better informed 

 than we are, it is therefore obvious that no general account 

 could be afforded within any moderate limits of space, so I 

 confine myself, as an example of what may be observed in 

 some one region, to the following sketch of a year's experience 

 on this point in the North-west Provinces of India, and 

 Oudh. Presuming a visitor to arrive in January, he would 

 find about houses and in gardens, but two species, C. 

 fafigans, Wied, and C. impellens, Walker, and even these, 

 neither troublesome, nor numerous. 



In the garden tanks he would find the larvae of these 

 species and also those of Anopheles Bossii, Mihi, and 

 sinensis, Wied, but, owing to almost all natural collections 

 of stagnant water of moderate size being already dried up. 



