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NOTES ON THE MOSQUITOS OBSERVED AT BOLE, 

 NORTHERN TERRITORIES, GOLD COAST. 



Bj De. A. Ingkam. 



West African Medical Service. 



Bole is a small town situated just north of the 9th parallel N. lat. and about 

 15 miles from the Black Volta, which forms the western boundary of the 

 Northern Territories of the Gold Coast. 



The town lies in a basin-like depression surrounded by ironstone ridges which 

 rise to a height of 300 to 400 ft. above the bottom of the valley ; a less elevated 

 spur projecting into the depression from the north-west gives the valley the shape 

 of a crescent. Bole is built at the foot of this spur very near the centre of the 

 concavity of the crescent. During the rainy season the water drains off the 

 surrounding ridges and collects in a swamp, which, following the contour of the 

 valley, forms a crescent round the town ; this swamp persists for about seven 

 months of the year, from the beginning of June to the middle of December. 

 Along the edges of the swamp and around either end the natives have dug 

 numerous water-holes. Many of these were made a generation ago when the 

 town extended over a larger area than it does at the present time, and though no 

 longer used by the natives they have not been filled in, so that they form ideal 

 breeding pools for mosquito larvae. The majority of these water-holes are 

 circular in shape, from 3 to 6 feet in diameter and 3 or 4 feet in depth ; usually 

 they contain perfectly clear water and frequently have masses of algae growing 

 in them. The country in the Bole valley is covered with orchard bush and 

 grass ; many of the water-holes have been dug at the base of trees, while towards 

 the latter end of the rains the grass has become so long as to overhang others, 

 so that excellent shade is afforded for the growing larvae. 



In addition to the water-holes there are several borrow-pits from which the 

 mud to form the huts of the town has been taken ; these are much larger than 

 the water-holes, being 20 to 30 yards in circumference and 3 to 8 feet in depth. 

 All these borrow-pits become filled with water during the rains, and this water 

 is more liable to contamination by animal excreta, as, owing to the less steep 

 banks, cattle prefer to drink at these pits rather than at the water-holes. The 

 surface of the water in the borrow-pits is usually covered with a luxuriant growth 

 of a certain plant which has succulent green leaves and trailing roots.* As 

 explained subsequently, in my notes on Mansonioides uniformis, the plant appears 

 to play an important part in the development of the larvae of this mosquito. A 

 single plant may attain a diameter of five inches and have roots six inches long ; 

 it therefore provides admirable shade for the developing larvae where there are 

 no overhanging trees or grass. 



Samples of water were taken twice weekly from several of the water-holes and 

 from the borrow-pits from the middle of June to the end of December, and the 



* [Mr. E. G. Baker, of the British Museum, has kindly identified this plant as Pistia stratiotes, 

 L., an Aroid which is widely distributed through Asia and Africa. — Ed.] 



