44 POPULAR SCIENCE MONTHLY. 



any evidence in favor of the popular view tLat tliey breed in damp 

 grass, dead leaves, and so on. 



Hence, in order to get rid of these insects from a locality, it 

 will suffice to empty out or drain away, or treat with certain chem- 

 icals, the small collections of water in which their larvae must 

 pass their existence. 



But the practicability of this will depend on circumstances — 

 especially, I think, on the species of mosquito with which we wish 

 to deal. In my experience, different species select different habi- 

 tations for their larvae. Thus the common " brindled mosquitoes " 

 breed almost entirely in pots and tubs of water; the common " gray 

 mosquitoes" only in cisterns, ditches, and drains; while the rarer 

 " spotted-winged mosquitoes " seem to choose only shallow rain- 

 water puddles and ponds too large to dry up under a week or more, 

 and too small or too foul and stagnant for minnows. 



Hence the larvae of the first two varieties are found in large 

 numbers round almost all human dwellings in India; and, because 

 their breeding grounds — namely, vessels of water, drains, and 

 wells — are so numerous and are so frequently contained in private 

 tenements, it will be almost impossible to exterminate them on a 

 large scale. 



On the other hand, spotted-winged mosquitoes are generally 

 much more rare than the other two varieties. They do not appear 

 to breed in wells, cisterns, and vessels of water, and therefore have 

 no special connection with human habitations. In fact, it is usually 

 a matter of some difficulty to obtain their larvae. Small pools of 

 any permanence — such as they require — are not common in most 

 parts of India, except during the rains, and then pools of this kind 

 are generally full of minnows which make short work of any mos- 

 quito larvae they may find. In other words, the breeding grounds 

 of the spotted-winged varieties seem to be so isolated and small 

 that I think it may be possible to exterminate this species under 

 certain circumstances. 



The importance of these observations will be apparent when I 

 add that hitherto the parasites of human malaria have been found 

 only in spotted-winged mosquitoes — namely, in two species of them 

 in India and in one species in Italy. As a result of very numer- 

 ous experiments I think that the common brindled and gray mos- 

 quitoes are quite innocuous as regards human malaria — a for- 

 tunate circumstance for the human race in the tropics; and Pro- 

 fessor Grassi seems to have come to the same conclusion as the 

 result of his inquiries in Italy. 



But I \vish to be understood as writing with all due caution 

 on these points. Up to the present our knowledge, both as regards 



