262 
ZOOLOGICAL GEOGRAPHY. 
[rART III. 
zoology, though there is reason to believe that it is a compara- 
tively recent intruder into the country. 
II. The West- African Sub-region. 
This may be defined as the equatorial-forest sub-region, since it 
comprises all that portion of Africa, from the west coast inland, 
over which the great equatorial forests prevail more or less unin- 
terruptedly. These commence to the south of the Gambia River, 
and extend eastwards in a line roughly parallel to the southern 
margin of the great desert, as far as the sources of the upper 
Nile and the mountains forming the western boundary of the 
basin of the great lakes ; and southward to that high but marshy 
forest-country in which Livingstone was travelling at the time 
of his death. Its southern limits are undetermined, but are pro- 
bably somewhere about the parallel of 11° S. Latitude. 1 
This extensive and luxuriant district has only been explored 
zoologically in the neighbourhood of the West coast. Much, no 
doubt, remains to be done in the interior, yet its main features 
are sufficiently well known, and most of its characteristic types 
of animal life have, no doubt, been discovered, 
Mammalia. — Several very important groups of mammals are 
peculiar to this sub-region. Most prominent are the great 
anthropoid apes — the gorilla and the chimpanzee — forming the 
genus Troglodytes ; and monkeys of the genera Myiopithecus 
and Ccrcocebus. Two remarkable forms of lemurs, Perodicticus 
and Arctocebus , are also peculiar to West Africa. Among the 
Insectivora is Potamogale, a semi-aquatic animal, forming a 
distinct family ; and three peculiar genera of civets (Viverridae) 
have been described. Hyomoschus , a small, deer-like animal, 
belongs to the Tragulidte, or chevrotains, a family otherwise 
1 Dr. Schweinfurth has accurately determined the limits of the sub-region 
at the point where he crossed the watershed between the Nile tributaries and 
those of the Shari, in 4^° N. Lat. and 284° E. Long. He describes a sudden 
change in the character of the vegetation, which to the southward of this 
point assumes a West-African character. Here also the chimpanzee and 
grey parrot first appear, and certain species of plants only known elsewhere 
in Western Africa. 
