XIV INTRODUCTION. 



where many species, especially of the latter order, congregate 

 in large numbers, and are found closely entwined together. 

 Here they pass the winter in a state of almost lifeless re- 

 pose, the functions of life so nearly suspended, that none of 

 the external signs of its existence are visible. The circula- 

 tion is extremely slow, the respiration apparently altogether 

 stopped, digestion absolutely suspended. The return of the 

 genial warmth of spring calls them again into action. The 

 circulation is restored, the blood is again fitted for its various 

 offices by the return of regular respiration, the functions of 

 the digestive organs are again performed, and the animal 

 resumes its former habits, without having undergone any 

 material change. 



I have already hinted at the difficulties which exist in 

 forming a consistent and unobjectionable arrangement of 

 these animals. The order of Testudinata and that of Lo- 

 ricata, — the former comprising the Tortoises and Turtles, 

 the latter the Crocodiles and their congeners, — are natural 

 and well defined ; nor is there any sufficient ground for iden- 

 tifying the latter group with the true Saurians. On the other 

 hand, the Saurians and the Ophidians are so nearly related 

 in all important points of their structure, and pass into each 

 other by such insensible gradations, that I cannot but think 

 that Merrem was correct in viewing them as constituting a 

 single order, to which he gave the name Squamata, from the 

 nature of their dermal covering. If the true Ophidians, or 

 Serpents, be considered as ordinally distinct from the Li- 

 zards, the intermediate group to which Mr. Gray has given 

 the name Saurophidia, must also constitute a distinct order ; 

 but I am rather disposed to follow Merrem's arrangement. 

 Adding, therefore, the EnalioHaurians of Conybcare, in- 

 cluding the great fossil reptiles, the Ichthyosauri and Plesio- 

 sauria, as a group probably intermediate between the Tor- 



