250 



THE DISTRIBUTION AND CHARACTERS OF REPTILES. 



between the toads Bufo regularis and B. garicpensis are far more 

 profound than those which are shown in their skins, and that 

 the external dififerences are only to be regarded as incidental 

 accompaniments of a different constitution. In the case of toads 

 it is obvious that natural selection must operate, especially during 

 their tadpole stages, and in the drier parts of South Africa, where 

 rains fall at rare intervals, and natural pools soon disappear, 

 there can be no doubt but that differences in the duration of the 

 tadpole life may ibe of life and death importance. Now I have 

 elsewhere endeavoured to show that in all probability the genus 

 Bufo came to South Africa from the North, in which case it 

 may well be that B. regularis represents the ancestral form in 

 South Africa. This being the case it will be of great interest to 

 know to what extent regularis and its presumed derivative garic- 

 pensis differ in the duration of their tadpole life, a question which 

 unfortunatelv I cannot answer. Nevertheless some careful 



REGULARIS 

 GARirPENSI5 



Distribution of Bufo gdricpciisis {xranlij and of Bufo rrxnlatis. 



observations made by J. H. Power, of Kimberley, show that Bufo 

 vertehralis, another prol^able derivative of regularis. an inhabitant 

 of the drier parts of the Cape, has an uiiusually short tad])ole 

 life, the period from deposition of eggs to the appearance of the 

 young toads covering only i6 days, which is the shortest ba- 

 trachian inetamorphosis known to me. This species moreover 

 can make use of muddy pools for its tadpole hfe, whereas regu- 

 laris seems to require running water. Such an adaptation can 

 be easily explained in terms of the natural selection theory, 

 though the possibility of a Lamarckian explanation must also be 

 considered, seeing that the development of tadpoles is so easily 

 accelerated or retarded by varying the temperatures. 



However, the differences between regularis and vertebralis 

 probably are not merely the result of differences in the periods of 

 development of the tadpoles, for according to observations made 

 by J. H. Power, the same species of frog { Raiia fuscigula) may 

 vary extremelv in this respect without showing any perce])tible 

 differences in the adults. When we consider the profound differ- 



