69 



perish in the unsuitable pools, or that the adults generally retiu-n to the same pools 

 in order to lay their eggs. It seems likely that the adults generally lay their eggs iu 

 the pools in which they themselves were bred, and that the insects thas learn by 

 experience the places most suitable for them. 



(7) Detection. — It is easy to overlook Anopheles larvae miless they are searched for 

 in a bright light. 



(8) Pupa'. — The pupse of Anopheles seem to be smaller than those of the com- 

 moner species of Culex. They require about forty-eight hours t<j reach maturitj' in 

 vitro; perhaps less in natural conditions. 



16. BIONOMICS OF ADULT ANOPHELES. 



(1) Ilaidting. — The adults generally hatch out in the evening; t)ut their exit seems 

 often to depend on the meteorological conditions of the moment, and appears to be 

 delayed by rainy and windy weather. 



-(2) Food. — They can easily be kept alive in glass cages, test tubes, bottles, etc. 

 We kept some in this manner for a f<jrtnight, and could doubtless have kept them 

 longer if we had wished to do so. We are able t(j confirm Bancroft's statement (18) 

 that gnats feed on bananas; but they seem to prefer the fresh fruit. During the day 

 the insects remained at rest on the walls of the cage, but in the evening began to 

 fly about and to walk over the fruit, plunging their j^roboscis into it in many places, 

 so that the banana was sometimes covered with gnats, both male and female. They 

 also drink water frequently, and each can often be seen to be distended with the 

 fluid. Raw meat was offered to them, but they could not be observed to touch 

 it. Earth placed at the bottom of the cage seems to ])e suitable f(jr them. 



According to the accounts of the soldiers at Wilberforce, they bite almost entirely 

 in the evening and night, but have been known to feed on men during the day. 

 They can certainly l)e fed on men artificially during the daytime, simply Ijy placing 

 them in test tubes and then apjilying the mouth of the tube to the skin. The stom- 

 ach can be observed to become distended in from one to two minutes or more; after 

 which the insect continues to suck, but commences to evacuate by the anus serum 

 containing a small percentage of red corpuscles. Culex voids only a clear fluid under 

 the same circumstances. The insects sometimes continue sucking like leeches for 

 five or ten minutes, voiding blo(jd all the while; but at other times soon withdraw 

 the proboscis and then try another spot. It was noted, however, that Anopheles 

 fed in this manner, even after they had remained sucking for five or ten minutes, 

 never showed an\' great distension of the abdomen ; while the contents of the stom- 

 ach still remained for some time transparent and red as seen through the scales of the 

 living insect. Moreover, in these cases the meal was generally digested or voided 

 within about twenty-four hours. 



On the other band, Anopheles which had fed themselves under natural conditions 

 generally presented a very different apjjearance. They were eiKjrmously distended; 

 while the contents of the stomach were thick, opaque, and black, and sometimes did 

 not disappear for three days. The only inference is that, under natural conditions, 

 the insects which can manage to do so gorge themselves over and over again during 

 the night — probably from the same subject. 



(3) Propagation. — We also observed that while naturally fed gnats invariably laid 

 eggs after two or three days, those which had been l)redfrom the larvae in captivity, 

 and had then been isolated and fed in test tubes, never did so, although before being 

 isolated they had long been in company with males. The inference is that fertiliza- 

 tion takes place only after the female has been fed. 



We noted also that in a cage where many male and female gnats, (Jnlex and A)to- 

 pheles, were kept together for weeks eggs were never laid, although the insects were 

 fed as described on Vjananas, and the cage contained water for them to lay their eggs 

 in. It seems, then, that a meal of blood is necessary before fertilization. 



