70 



Lastly, we observed that previously fed and fertilized insects would lay a second 

 batch of eggs after a second meal of blood without a second fertilization, but never 

 laid a second batch of eggs without a second meal of blood. That is, one fertiliza- 

 tion suffices for several batches of eggs, but one meal of blood for only one batch of 

 eggs. 



These observations are wholly in accord with the results of the prolonged study of 

 many kinds of gnats made in India by one of us; and it therefore seems likely that 

 the following law is likely to hold good for the CuUcidx which feed on men, at least 

 for the conniioner species. 



Although these gnats can live indefinitely on fruit and perhaps juices of plants, the 

 female requires a meal of blood, both for fertilization and for the development of her 

 ova. In other words, the insects need blood for the propagation of their species. 



Blood was never found in male Culicidse in Freetown, according with the general 

 law. 



(4) Haunts. — The large majority of Anopheles caught by us in dwellings were 

 females which were generally much gorged, and, if fed at all, were invariably fertil- 

 ized; in other words, the males and unfed, or only slightly fed, females do not gen- 

 erally remain in the houses during the daytime, or if they did remain, kept in the 

 roofs or other dark places where they were little observed. On the whole, we think 

 that only those females which are so gorged that they can not fly far remain in the 

 houses during the day. AVe observed that if a cage full of Anopheles was disturbed 

 •in the daytime, the insects always struggled toward the light as if to fly out from 

 the windows, and several which escaped from the cages actually did so. On one 

 occasion a large number escaped from their cage during the night in the rooms occu- 

 pied by one of us; none of them could be seen next morning. 



Yet we may be quite sure that both the males and the unfed females haunt the 

 houses during the night. The invariably fertilized conditions of the gorged females 

 caught in the houses show that the males must be present in the houses when the 

 females feed, since the latter are often so much distended after feeding that they are 

 obviously unwilling to fly even a few feet from the bed of their victim; in other 

 words, fertilization must take place within the houses. The unfed females must, of 

 course, resort to human habitations during the night in order to obtain their fo(Hi 

 at all. 



These facts would seem to indicate that in Freetown in the rainy season the 

 Anopheles resort to the houses during the night, but that all except the gorged females 

 live elsewhere during the daytime — possibly sleep in the trees and shnibs. The 

 point is of interest as tending to show that large numbers of Anopheles may be present 

 in a dwelling during the night, without it being easy to find them during the day. 



It should, however, be added that in India males and unfed females were often 

 found in the houses in large immbers by one of us. Possibly different species have 

 different habits in this respect. 



Several old residents of the country informed us that gnats are usually very preva- 

 lent in the presence of much vegetation — especially long grass and undergrowth. 

 Though it is difficult to see how such can favor the larvse, we can understand that 

 much vegetation can shelter the adults of certain species, which may even feed on 

 particular kinds of plants when they can not obtain blood, and may consequently 

 find it easier to live where these plants afford them both food and shelter than else- 

 where. It must also be remembered that gnats can certainly bite birds and other 

 mammalia besides man; and that such are apt to congregate where there is much 

 vegetation. On the whole, then, there is nothing improbable in the idea that the 

 Freetown Anopheles should li\'e outside the houses in the daytime. 



o 



