224 J. W. SCOTT MACFIE. 



hatched from eggs laid by different parents. In the case of the rarer species, 

 however, it has significance, since it must often be very difficult, one would think, 

 for a male hatched in one place to find a female that was not the offspring of the 

 same mother. This is especially true in mosquitos such as Stegomyia which, in 

 captivity at any rate, pair very soon after emergence from the pupae. After hatching 

 they generally rest for a time close to the place where they find themselves oii 

 emergence, and sometimes indeed they pair as soon as they rouse themselves from 

 this rest. 



The arrest of development observed in larvae bred in the laboratory. 



The period of the life-cycle of Stegomyia fasciata varies considerably. The eggs. 

 under normal conditions generally hatch in three to four days, the larval stage 

 usually lasts from seven to thirteen days, and the pupal stage one to five days. 

 It is well known, however, that imder certain conditions the duration of the cycle 

 may be greatly extended. Francis, for instance, has shown that the eggs may remain 

 viable for as long as six and a half months, at an}^ rate if they are kept dry ; and 

 it must be the experience of everyone who has bred S. fasciata to any considerable 

 extent that the eggs, even when left lying on the water, may remain dormant for 

 a long time. Unlike the eggs of Culexfatigans, which generally hatch all at the same 

 time, those of >S'. fasciata hatch one by one, or two or three at a time ; and 

 consequently most samples of larvae of this species sent for examination include 

 individuals at various stages of development. No attempt has been made ta 

 determine the limits of the period of viability of eggs left lying in or on the water 

 where they were laid, but I have notes of one experiment in which from eggs laid 

 on 14th June perfectly healthy larvae (which eventually developed into adults) 

 hatched on 20th July, the 37th day. 



The larval stage also may be greatly prolonged. Even at the temperatures of the 

 laboratory at Accra (average about 80° F.) it may sometimes extend far beyond the 

 time accepted as the normal. 



In the samples of mosquito larvae sent to the laboratory by the Medical Ofiicer 

 of Health an arrest of development is a common phenomenon. This is often 

 troublesome, for it is easier, and more reliable, to identify adults than larvae, 

 especially in the genus Stegomyia ; and whilst waiting for the larvae to pupate and 

 hatch, an unmanageable collection of bottles and jars is apt to accumulate. One 

 larva of Stegomyia luteocephala was kept in this way for 53 days, as I was anxious 

 to obtain another specimen of the adult m^osquito, but eventually the hope was 

 given up, and the larva was killed and preserved. 



Of the larvae sent to the laboratory those of Stegomyia generally pupate and 

 hatch quickly, those of Culex frequently die, and both alike are subject to the delayed 

 development referred to above. The larvae thus arrested appear to be fully 

 mature, but for some reason unwilling or unable to undergo the transformation 

 into pupae. They have ceased to moult, and to the naked eye look perfectly healthy. 

 It will perhaps be impossible to determine the maximum duration of the larvaL 



