398 ZOO-GEOGRAPHICAL NOTES. 



allied varieties, and to this end the regions of moist, warm, 

 dense forests should chiefly be searched. Heuglin, though 

 furnished with comparatively insufficient material, has already 

 pointed out that, as we advance from the north in the direction 

 of the equator, the affinities of the north-eastern fauna with 

 that of the west, and even of the south, grow more numerous, 

 that is, a number of varieties formerly believed to belong 

 exclusively to the west spread themselves much farther to 

 the east than has generally been supposed. My owu col- 

 lections confirm this opinion most thoroughly, and I will 

 attempt to show that the reason of it is to be found in the 

 physical formation of the country and the vegetation which 

 clothes it. 



Soon after the Bahr-el-Jebel has passed the rocky defile of 

 Jinja, after leaving the Victoria Lake, and has spread itself 

 out in the wide alluvial plains of eastern Unyoro into a series 

 of shallow, lake-like basins, it is again confined by mountain 

 ranges, and flows between high rocky banks over a succession 

 of steps, which form rapids, to the Mwutan Nzige or Albert 

 Lake. Except the extensive swampy flats to the east of 

 Mriili, which are exposed to the inundations of the river, 

 and the equally flat tracts of the southern Lango district, 

 which in some places extend to the river, and are covered 

 with a vegetation of grass and papyrus peculiar to such boggy 

 districts, both banks of the river are overgown with thick 

 forest. On the northern bank, in consequence of less abun- 

 dant irrigation, greater declivity, and a very insignificant 

 thickness of surface soil, the leathery-leaved and stiff forms 

 of northern vegetation prevail, which are not affected by tem- 

 porary droughts. The southern bank, on the contrary, pre- 

 sents a succulent verdure, and a rich display of foliage 

 belonging to tropical species and dependent on constant 

 moisture. Though the region between the lakes, a decidedly 

 mountainous country, cannot produce the exuberant vegetation 

 of the western tropics, owing to its elevation, yet the dews, 

 continuing all through the year without intermission, and the 

 exceedingly rich and well-watered soil, supply a basis for a 

 considerable development of vegetable growth. Besides the 

 imposing representatives of northern latitudes, the Ficus, Bal- 



