IHE DISTRIKUTTON AND CHARACTERS OF REPTILES. 25 1 



ences of environment wliich characterise the different regions 

 in which our closely allied species are isolated, it cannot be 

 doubted but that their physiological processes are not (|uite the 

 same, which of course implies ada])tation in the specific physio- 

 logical characters. Such species physiologically, as well as mor- 

 phologically, are distinct entities. On the other hand, if several 

 species may arise as a result of isolation within a uniform envi- 

 ronment, there can be no adaptational differences whatever 

 between them. Dift'erences in habit between allied species which 

 inhabit the same locality probably imply constitutional dift'er- 

 ences, and so far as we can judge, may have no direct relation to 

 the structural characters separating the species. 



Closely allied species which on the whole occupy distinct 

 regions are sometimes found to overlap considerably in their 

 distribution, but even then the specific peculiarities of habit may 

 often be seen. Dr. R. Broom gives a very suggestive case when 

 dealing with the golden moles.* Chrysocliloris asiatica occurs 

 commonly in tlie Cape Peninsula, and passes eastwards as far 

 as Bredasdorp and .Swellendam. C. hotteniota occurs from 

 Stellenbosch to Zululand. He says : 



At Stellenbosch, both C. liotientota and C. asiatica are found in the 

 same gardens, but they apparently keep certain regions to themselves. 

 Thus in my garden C liotientota is the species commonly met with, while 

 across the road in the college quadrangle C. asiatica most commonly 

 occurs. It appears probable that C. asiatica prefers the drier and sandier 

 soil and C. hottentota the richer garden soil. The breeding season of C. 

 hottentota appears to be later than that of the smaller mole. 



Later on he points out that though Stellenbosch is separated 

 from the Cape Peninsula by only about twenty miles of rather 

 sandy soil, C. hottentota has not been found at Capetown, where 

 C. asiatica is common. It would appear that these two species 

 are adapted to minor differences of the environment. 



The hypothesis of the close physiological adaptation of 

 species to a particular environment must imply that a particular 

 species will not be able to persist permanently as such if removed 

 from its own environment and placed within that of its ally. 

 Tested in this way, the hypothesis might not be of verv wide 

 application, and Mr. Bateson has, emphasised the fact that at the 

 present day the fit of an organism to its environment is not after 

 all very close. Bateson's statement is no doubt correct in numer- 

 ous cases, but it must be clearly emphasised that the hypothesis 

 only relates to the case of closely allied species geographically 

 separated in different physical environiuents. It seems to me 

 worthy of serious consideration as a factor in evolution, as it 

 helps to afford an explanation of the beginnings of discontinuity 

 between species when structural adaptations are not included in 

 the specific characters : for firstly, through physiological adapta- 

 tion to different environments the same stock tends to become 



Trans. S.A. Phil. Soc. (1907). 18. 296. 



