494 THE SNAKES OF SOUTH AFRICA. 



he was obliged to lie down for hours at a time. These symptoms 

 grew less and less severe as time wore on, and have now almost 

 disappeared, although at times when he is out for long in the 

 hot summer sun, he feels faint and dizzy. 



Although the snake escaped, there is no doubt about it being 

 a Boomslang, as Pretorius knows a Boomslang as well as I do. 

 He informs me that the snake ghded up a dense mass of prickly 

 pears and rapidly slid away out of sight amongst them. Tliis 

 is rather remarkable when it is rcaUzed that a hedge of prickly 

 pears is smothered with long, sharp, straight thorns sticking out 

 at all angles. 



E. 



The Isolation of Madagascar and Australia. 



There is very strong evidence for believing that Madagascar 

 was, in remote times, joined to the mainland of Africa, and that 

 Austraha was a part of Asia. Now, even the study of snakes 

 helps us in coming to such a conclusion, and even suggests the 

 period at which the separation took place. 



In Madagascar there are no front-fanged [Proteroglypha) 

 snakes such as the Vipers and Cobras. They are all of the 

 hind-fanged {Opisthoglypha) and sohd-toothed {Aglypha) species. 

 This indicates that snakes had not evolved a typical poison 

 apparatus prior to the separation of Madagascar from Africa, 

 otherwise we should have found them there, for Africa is teeming 

 with the front-fanged species of snakes. This fact leads us to 

 conclude that ^Madagascar was isolated at a very remote period 

 of time, and that the separation of Australia from the mainland 

 of Asia occurred at a more recent period, because we find numbers 

 of species of front-fanged, typically venomous snakes in tliat 

 country. We thus infer it was isolated after snakes had fullj^ 

 evolved their poison apparatus. 



^Moreover, in Australia, there are no snakes of the viper (adder) 

 family, although there are plenty of them on the mainland of 

 Asia. Tliis fact would seem to indicate that the viper family 

 of snakes have evolved at a more recent period than the Colubrine 

 group of venomous snakes. 



Further, snakes have never been known in New Zealand. 



