170 J. W. SCOTT MACFIE AND A. INGRAM. 



In the Annual Report of the Accra Laboratory for the year 1914 the records of the 

 examinations of mosquito larvae from 1912 to 1914 were similarly dealt with and the 

 distribution of the specimens amongst the various blocks was shown in tabular form. 

 Nine samples containing Anopheline, 282 Stegomyia, and 74 other Culicine larvae 

 were thus located. By combining these with the 1915 specimens we were able to 

 locate the blocks in which 13 samples containing Anopheline larvae, 610 containing 

 Stegomvia larvae, and 139 containing other Culicine larvae had been found (see 

 Table V.). 



The distribution of these samples is shown by means of conventional signs on the 

 attached map (Map I). This map has been prepared from the latest map of Accra, 

 and on it the various blocks into which the town is divided are marked and numbered, 

 but for the sake of clearness almost all other features have been excluded. As the very 

 small number of samples found to contain Anopheline larvae would have been entirely 

 lost amongst the Stegomyias had each sample of larvae from each block been repre- 

 sented by a separate sign, some means had to be devised by which the numerical 

 distribution of the larvae could be shown approximately without allowing one type 

 to obUterate another. It was found that this could best be done by using one sign for 

 every ten entries ; thus one solid circle in any block indicates that Anopheline larvae 

 have been found in this area, but that less than eleven such samples have been 

 received, or two crossed circles in a block indicate that any number of samples of 

 Stegomyia larvae from eleven to twenty have been received from this area. Both 

 Anopheline and other Culicine larvae therefore figure in this map in undue proportions, 

 but it was necessary to allow this to occur, as in their true proportions they would 

 have been hardly distinguishable. 



Looking at this map then we see that mosquitos breed most freely in the middle of 

 Accra in the neighbourhoods of blocks iv and ^ai. This part of the town is crowded 

 with native compounds, and is the most densely populated. In the outskirts of the 

 town and in the village of Christiansborg relatively fewer larvae are found, a fact 

 readily accounted for by the less congested nature of these districts. 



With regard to the distribution of species, Stegomyia, which practically means 

 S. fasciata, occurs in every block in proportions such that it altogether outnumbers 

 all others. Culicine larvae, that is practically Cidexfatigans, occur in smaller numbers 

 in every part of Accra, and in six of the seven blocks of Christiansborg. Anopheline 

 larvae, that is Anopheles costalis, on the other hand have only been found in very 

 small numbers, once or twice in a block, but they have been received from all the 

 blocks with the exceptions of blocks i, ii, v, vi, xii, and xiii of Accra, and blocks i, iii, v, 

 and vii. of Christiansborg. How it is that Anopheles costalis comes to be found 

 breeding in the compounds in water-receptacles is not quite clear. It has been 

 suggested that owing to the arid nature of Accra the mosquitos are compelled to 

 deposit their eggs on water contained in domestic vessels for lack of a more favourable 

 situation, but there are in the neighbourhood of the town pools suitable for the 

 breeding of Anopheline mosquitos, and in which as a matter of fact the larvae of 

 A. costalis are generally to be found. Graham at Lagos similarly found this mosquito 

 breeding in " the domestic pots and barrels of native yards," and as Lagos cannot 

 be called arid, it seems probable that A. costalis does voluntarily breed in such 

 situations. Graham, however, notes that there was a rise in the percentage of vessels 



