NOTES ON THE DISTRIBUTION AND CHARACTERS 

 OF REPTILES AND AMPHIBIANS IN SOUTH 

 AFRICA, CONSIDERED IN RELATION TO THE 

 PROBLEM OF DISCONTINUITY BETWEEN 

 CLOSELY ALLIED SPECIES. 



By John I-Iewitt, B.A. 



( ll'itli Four Maps.) 



The data for the study of geographical distribution of 

 animals in South Africa are rapidly becoming obscured as a 

 result of the operations of civilised man. Amongst the terres- 

 trial vertebrates, probably the reptiles and 1)atrachians are now 

 most suitable for zoogeographical studies, as their natural 

 distribution has not been so radically modified through human 

 agency as is the case with the higher vertebrates. 



Through the work of the late Dr. Bolus and others, 

 botanists are well acquainted with the broad facts of plant 

 distribution in South Africa, and as animal and plant life are 

 so closely associated and mutually dependent, it may be inferred 

 that some correspondence must ol)tain in their manner of dis- 

 tribution. The facts are as follows : the orders and genera of 

 flowering plants separate tlicmselves into a number of well- 

 defined botanical regions, but the families and many of the 

 genera of reptiles range throughout the sub-continent, and only 

 in a very loose way may we distinguish two areas, an Eastern 

 and a Western, partly separated by the Drakensberg Range: 

 nevertheless, the species of polytypic genera of reptiles do in 

 some cases arrange themselves into areas which roughly coincide 

 with the various floral regions, but in other cases the species 

 of a genus occupy areas which seem to have no relation with 

 botanical regions. The exact distribution of all these species 

 and the nature of the characters which separate them from 

 their nearest allies, may be expected to afford important data 

 bearing on the great question of the origin of species. Some 

 of the contested problems we may hope to investigate are : ( i ) 

 What is the importance of Isolation, geographical or topo- 

 graphical, as a factor in the formation of species? May several 

 species arise from the same stock within a uniform environ- 

 ment provided that several portions of that environment are 

 separated from each other by barriers? (2) What is the 



evidence for and against mutations as opposed to the older 

 view of a gradual evolution through more or less minute and 

 fluctuating variations? (3) Are .specific characters adaptative? 



Isolation as a factor of primary importance in the evolution 

 of species. This view has been vigorously championed bv 

 Wagner, Romanes and Gulick. and by many systematists. 



The term Isolation may be used in reference to all the 

 various factors which prevent the interbreeding of two groups 



