INTRODUCTION. 



Reptiles axd Batrachians. 



The Reptiles and Batracliians belong to what ar6 ciMiimonly called the 

 vJoUl-blooded Vertebrates. This name is ai^plied because the heat-pro- 

 ducing capacity of their bodies is so low as to render them very susceptible 

 to thernral A'ariation in the surrounding air or water, and unable to main- 

 tain any standard temperature. In Batrachia that breathe by means of 

 gills, the small amount of heat the body is capaljle of iiroducing is limited 

 by the amount of oxygen in the water. A heart in which ventricles or 

 atria ;ire more or less incompletely separated mixes venous with the 

 arterial blood supplied the tissues of lung-bearing Reptiles and Batrachi- 

 ans; and thus, in consequence of })artial oxygenation, their heat-producing 

 capacity is reduced. Animals of these classes are, to a considerable 

 extent, dependent on external heat; they are more active during the 

 warmer portions of the season or of the day. During the winter of the 

 temperate zones or the dry season of the tropics they are comparatively 

 inactive. 



The Turtles, Crocodiles, Lizards, Amphisbaenians, and Snakes are Rep- 

 tiles. They are hatched or born with the shape of the adult, breathe by 

 lungs, and generally are covered by a skin the outer layers of which are 

 folded so as to resemble scales. The Batrachians include such as the 

 Toads, Frogs, Salamanders, Newts, Sirens, and Ciecilians. Nearly all of 

 them breathe and progress like fishes during the earlier portion of their 

 existence, and the majority go through a metamorphosis, taking on the 

 form of the adult and breathing by lungs later in life. They are without 

 the scale-like folds of the Epiderm. 



From the Turtles to the Snakes of the one, and from the Frogs to the 

 worm-like Csecilians of the other of these classes, there is a great diversity 

 of forms and habits. In all the intelligence is of a low order. Commonly 

 one or more of the senses is feebly or not at all developed. Many are slow 

 in growth, and live to great ages. Most are tenacious of life, and able to 

 do without food or drink for long periods. The greater portion are harm- 

 less; the exceptions are such as the Crocodiles, the few venomous, and a 



