PROBLEMS AND RELATIONS 3 



It is absent in part of Mozambique and only reappears to the north 

 of Rovuma, extending thence to Senegambia. The black rhinoceros 

 originally ranged to the extreme south of Africa. Its southward range 

 is now much restricted, and it extends no further west than the Niger. 

 Zebras also formerly ranged to the Cape, but did not go so far west 

 as the rhinoceros. The giraffe appears to be absent in British Central 

 Africa, while the zebra is present. The eland extends beyond the 

 Zambezi-Congo divide; most of the savanna mammals do not. Buffa- 

 loes are absent in Somaliland, lions in the Cameroons. 1 Much remains 

 to be done in defining the ranges of individual species, and exact 

 knowledge of these is required to complete the foundation for 

 zoogeographic investigations. 



The principal avenue of approach to faunistic zoogeography is 

 systematic zoology. Intensive systematic studies have unearthed new 

 problems for zoogeography. Of prime importance is the recognition 

 of the fact that many widely distributed animals have a different 

 appearance in the different parts of their range, and are divisible into 

 geographic subspecies by means of constant minor differences, in spite 

 of their general agreement in important characters. 2 Some compre- 

 hensive species of this type are the wall lizard {Lacerta muralis), 

 the African lion, the puma, the wild turkey, the song sparrow, the 

 king snake, and, among butterflies, the yellow swallowtail (Papilio 

 turnus). Subspecies of such species may be sharply defined; but they 

 may also be united by intermediates so that it sometimes requires 

 the practiced eye of a specialist to distinguish them. The recognition 

 of these minor geographic differentiations is of importance for the 

 study of the influence of external conditions upon animals. Many 

 detailed studies of this nature have been made, especially for birds 

 and mammals, and the work of the systematists in this field, though 

 frequently regarded as trivial, is especially valuable. It is, of course, 

 to be desired that a uniform nomenclature and a definite characteriza- 

 tion of these geographic subspecies be introduced. This is furnished by 

 the trinary system of nomenclature; among song sparrows, for ex- 

 ample, the listing of Melospiza melodia melodia and Melospiza 

 melodia atlantica makes it immediately evident that the forms men- 

 tioned belong to a "Formenkreis." The term Formenkreis has become 

 current to distinguish series of allied forms whose distinction is geo- 

 graphic, and whose origin may be supposed to be entirely or primarily 

 due to geographic isolation. 



1 Superior numbers refer to the respective items in the Bibliographies at the 

 end of each chapter. See p. 10. 



