South African Tortoises. 411 



Eastern and South Western Regions of Bolus are the home of 

 nreoJatuH, his Karoo Region contains houlengrri, the Upper 

 Region is characterized 1)}^ feiiioralis, in the Western Region 

 bordering on the Kalahari Region is found s/^na^i/s, while f^arZm^r/ 

 in Mashonaland is in a different region from these. The 

 suggestiveness of the facts already established are sufficient to 

 warrant the prosecution of the enquiry ; they lend su})port to the 

 recent dictum of President D. S. Jordan' : " In nature a closely 

 related distinct species is not often quite side by side with the old. 

 It is simply next to it, geographically or geologically speaking, and 

 the degree of distinction almost always bears a relation to the 

 importance or the permanence of the barrier separating the 

 supposed new stock from the parent stock." 



It is questionable how far any of the characters relied upon 

 as of specific value can be considered as adaptive or helpful to the 

 animal in the struggle for existence. The colours vary from 

 yellow and green through brown to black, and may be partly 

 protective to the individual when walking over the veld, or resting 

 partly hidden undei- vegetation or rocks ; the femoral tubercles are 

 ceitainly protective, covering as they do an otherwise vulnerable 

 part of the creature when retracted. It can, however, scarcely be 

 of much importance to the individual animal whether it has four 

 or five claws to the fore limbs, large or small inguinal shields, a 

 few large or- many small head shields, or slightly larger or smaller 

 jilastial shiekis. The s)>ecific characters are probably best regar- 

 ded as expressions of tendencies along certain lines of develop* 

 ment which have now Income more or less fixed in the different 

 si)ecies as a result of isolation and a(la])tation, and can be i-elied 

 upon for taxonomic pui'i)()Ses 



KXI'LAN.VITON OF PLATE XI. 



Fig. 1. HoHiojJKs l)()ulch(j('ri. Ventral view. 



Fig. 2. Hoiiioptis houletKjcri. Side view. 



Fig. 3. Head scales on H. darliHjji. 



Fig. 1. „ „ H. areolatus. 



Fig. 5. „ „ H. boidengeri. 



Fig. (). „ ,. H. frmoralis. 



' " The Origin of species througb Isolation." Science, p. 546, Nov. '6, 1905. 



