﻿RESEAECH IN BRITISH WEST AFRICA. 145 



tropical rain forest and, on the other, so far to favour tree-growth that a wood- 

 land formation can still successfully compete against grass forms such as savannah 

 forests. Such conditions are realised in Southern Nigeria along an irregular, 

 tortuous, comparatively narrow belt that lies, roughly speaking, between the 7th 

 and 8th parallels in the Western Province, and between the 6th and 7th in the 

 Central and Eastern Province. This belt is pushed far up north in the extreme 

 north-east portion of the Western Province where numerous hill ranges carry a 

 copious rainfall well into the comparatively dry interior." 



Savannah forest is variously described as " park-like " or " orchard-like," and 

 consists chiefly of tall grasses with numerous terrestrial herbs and a few deciduous 

 trees, which are, on an average, less tall than in the mixed deciduous forest. The 

 number of trees varies in different places according to the nature of the soil and 

 the general situation, e.g., on laterite outcrops they are few in number and stunted, 

 while in valleys they are more numerous and healthy. These areas are generally 

 devastated by huge forest fires towards the end of the dry season, and this tends 

 to reduce them from the savannah-forest type to the pure savannah, where trees 

 are practically absent, and where grass tends more and more to predominate over 

 the terrestrial shrubs. 



Mangrove thickets are everywhere to be found along the coast, in the various 

 lagoons and backwaters, and in the innumerable creeks and rivers in the delta of 

 the Niger. This type of growth is associated with brackish water and muddy 

 swamp, and is exclusive in character, permitting no intrusion of other trees. 



These are the main types of vegetation in Southern Nigeria, and without 

 entering into details at present, that being reserved for fuller discussion under the 

 various regions, it might be well to point out in a general way how these different 

 types are associated with the distribution of the various species of Glossina. 



G. palpalis is to be found everywhere in the mangrove thicket area, and it is 

 especially noteworthy that in such regions the specimens are larger and darker in 

 colour than in other situations. This species is also the predominant one in the rain 

 forest and in the fresh-water swamp forest. 



G. caliginea seems to be confined almost entirely to the mangrove belt. 



G. longipalpis is the species most abundant in the mixed deciduous forest 

 region, while in the savannah forest G. tachinoides is most likely to be found. 

 As to the other species found in Southern Nigeria, the data available do not 

 justify any definite conclusions being drawn, but the records given throughout 

 the narrative will serve to show how far these species are associated with the 

 different types of vegetation. 



II. Climate and Eainfall. 



As is well known, climate and rainfall have a marked bearing on the distri- 

 bution of the various species of blood-sucking insects, and further, certain species 

 show distinct local modifications which are associated with the comparative 

 lengths of the wet and dry seasons, the range of temperature, and the degree of 

 25110 C 



