232 



ELEMENTS OF SCIENCE 



signification of the words to which they give utterance, 

 and which they evidently take pleasure in repeating. 



All birds have two pairs of limbs, but many reptiles 

 have none, and serpents creep over the ground by the 

 aid of their numerous and very movable ribs, while their 



FIG. 47. 



THE DEVELOPMENT OF THE FROG FROM THE TADPOLE. 



1 to 7, successive stages. 2, with external gills, which have 

 disappeared in 3. 



excessively distensible jaws enable them to swallow 

 creatures of very large size, compared with that of their 

 own head and neck. 



Reptiles are not normally able to raise the tempera- 

 ture of their bodies above that of the atmosphere they 



