PLAGIOTREMATA OPHLDIA. 207 



The Heptilia of the cold and temperate regions fall into a sort of 

 winter sleep, and in the hot climates there is a summer sleep which 

 comes to an end with the beginning of the rainy season. 



Most Reptiles are very tenacious of life, and can exist a long time 

 without food and with limited respiration, and are capable, though 

 in a less degree than the Amphibia, of reproducing injured or lost 

 parts of the body. 



The oldest fossil remains of Reptiles belong to the Primary period, 

 but appear only very sparingly in this period, being confined to the 

 Kupferschiefer formation (Proterosaurus Speneri). The Secondary 

 period (Trias and Jura) can show a far greater variety of forms. At 

 this time the Saurians and Hydrosaurians were predominant. The 

 scaly Lizards first appear in the upper strata of the Jura, and are 

 most abundant in the Tertiary period, which also presents a few 

 remains of Snakes. Chelonia first appear excepting the doubtful 

 footprints of the Trias in the Jura. Land-Tortoises are first met 

 with in the Tertiary formations. 



Sub-class l.-PLAGIOTREMATA (LEPIDOSAUBIA;. 



Reptiles with scales and dermal shields, either apodal or provided 

 with extremities. They have a transverse anal slit and a double penis. 



Order 1. OPHIDIA* (SNAKES). 



Apodal Plagiostremata without pectoral girdle ; with bifid protrusi- 

 ble tongue ; usually with freely movable, always displaceable, maxil- 

 lary and palatine bones ; without urinary bladder. 



The Snakes are chiefly characterized by the absence of extremities, 

 and by the distensibility, sometimes extraordinary, of the mouth 

 and pharynx. They cannot, however, be sharply separated from the 

 Lizards. Formerly the limitations of this order rested entirely on 

 the absence of extremities, and thus not only were the Cceciliadce 

 amongst the Amphibia, but also the Blindworms and other genera 

 of apodal Lizards, included in it. The Amphisbcenidce also were 



* Gray, " Catalogue of Reptiles in the collection of the British Museum." 

 Part III., Snakes. London, 1849. 



Giinther, " Catalogue of Colubrine Snakes in the collection of the British 

 Museum," London, 1858. 



Jan, " Tconographie gene'rale des Ophidiens," Livr. I. XXVII. Paris, 

 18601868. 



Lenz, " Schlangenkunde," 2 Auflage, Gotha, 1870. 



