260 THE REPTILES 



its head gently against our faces in the most affectionate manner, 

 but would draw away and hiss at strangers. The skin was cast 

 periodically, and for a day or two before this took place the Boa 

 appeared unwell and rather morose, but it quickly regained its 

 normal good temper and health once the old skin had been 

 sloughed off. 



It would be impossible here to enter into a detailed account 

 of the ancestors of the existing Reptiles ; their fossil remains 

 have been found in the Permian deposits, and in those of the con- 

 secutive ages to the Pliocene, but the Trias, Lias, and Oolitic 

 strata in the Old World, and the Cretaceous strata of the Old 

 and New Worlds, contain the greatest number, and the struc- 

 tural affinities of the extinct kinds with the recent, and with fish 

 and birds, are very remarkable. During the Mesozoic or Secondary 

 Period of the earth's geological history we find the reptiles occupy- 

 ing the place in the economy of Nature which has since been 

 usurped by the mammals and birds. This Secondary Period has 

 been aptly called the Age of Reptiles, and during that period 

 there existed gigantic forms which were vegetable feeders, as 

 ponderous as the extinct ground-sloths of the later Tertiary 

 Period ; there were slim, active carnivora, and great sea 

 reptiles with paddles formed solely for swimming, and there 

 were true flying reptiles, veritable dragons of the air, with well- 

 developed wings supported by bones of a texture and construction 

 now typical of the birds. 1 



1 For a popular introduction to this fascinating subject the reader should consult 

 the pages of Sir E. Ray Lankester's " Extinct Animals " ; the " Guide to the Fossil 

 Reptiles, Amphibians, and Fishes," of the British Museum (Natural History), price 

 ninepence ; and Dr. Hans Gadow's volume of " Amphibia and Reptiles," in the 

 Cambridge " Natural History." 



