6 BRITISH SERPENTS. 



animal types, the class Reptilia is one of absorbing 

 interest. Standing, as it does, next to the amphibians 

 on the one side and to the birds on the other, the 

 reptiles show a distinct relationship to both ; so that 

 there is found in them a further development of a 

 type of structure first seen in the amphibians, and 

 at the same time indications of features which appear 

 in greater perfection in the birds. So much so, indeed, 

 is this the case that reptiles and birds have been 

 classed together as a single series of animals under 

 the one name Sauroj)sida. Thus we see that " no one 

 class of vertebrates stands alone by itself. Every 

 year fresh researches by palaeontologists and the re- 

 examination of living vertebrates, especially in their 

 embryonic history, prove that no single class, not even 

 a type so well circumscribed as the modern birds, is 

 without links, forming genetic bonds, allying them 

 all together. The different classes of vertebrates, as 

 well as of other branches of the animal kingdom, 

 form an ascending series." ^ 



In the class Eeptilia we find some members which 

 are equally at home in water or on land, or which 

 spend part of their time in one element and another 

 part on the other. Our own common ring snake, 

 though a capital swimmer and fond of water, is 

 mainly a land serpent; while our adder, as a rule, 

 is averse to water, and is but rarely found at all in 

 damp places. 



^ Packard. 



