250 INTEODTJCTION TO ZOOLOGY. 



The number of species belonging to each of these orders is 

 very different, and may be thus stated : * — 



Tortoises (Testudinatd) 69 



Lizards (Saurid) 203 



Serpents {Ophidia) 265 



Frogs ( A mphihia 120 



657 



It is interesting to remark the manner in wliich, according 

 to Berghaiis, the number of species diminishes as we pass 

 from the sunny regions of the East to the duller and more 

 cloudy climes of Western Europe. Thus Italy with her 

 islands can number forty-seven species ; France has thii'ty- 

 one ; Great Britain, fourteen ;t and Ireland, it may be added, 

 not more than five. 



It has been stated that the blood of reptiles is cold, or in 

 other words, their power of producing animal heat is so feeble, 

 that we do not notice any difference between the temperature 

 of their bodies and that of the air or water by which they are 

 surrounded. The same was observed in the preceding group 

 of cold-blooded Vertebrata — the fishes — but arose from a dif- 

 ferent cause. In the fishes the blood is imperfectly aerated, 

 owing to the small quantity of oxygen with which it comes in 

 contact in the gills. In the highest of the reptile tribes, which 

 breathe exclusively by lungs, these organs are supplied with 

 only a portion of the blood that has circulated through the 

 veins ; the other portion is returned into the circulation with- 

 out being purified by exposure to the air. ' The arteries con- 

 sequently contain a mixtiu-e of blood rendered impure by its 

 previous circulation, and blood recently aerated in the lungs. 



* Berghaiis and Johnston's Physical Atlas, from which admirable work 

 all the information here given, as to the distribution and number of species, 

 is derived. 



f Namely, two Turtles, two Lizards, one Blind-worm, two Snakes, two 

 Frogs, two Toads, and three Newts 



In a IMemoir read before the Royal Society, by Mr. Higginbottom, 

 entitled, "Researches to determine the number of species and mode of 

 development of the British Triton, the autlior stat'^ that only two species 

 of Tritons or Newts are met witli in England, anur (hat the animals require 

 four years to attain their full gi-owtli. "The Triton," he remarks, "pos- 

 sesses the power of reproducing its lost limbs, provided the temperature be 

 within the limits of 58° and 75° Fahrenheit ; but at lower temperatures, and 

 during tlie winter, it has no sucli power." — Athena;um, April 3, 18-17 ; An- 

 nals of Natural History, July, 1847. 



