537 



CHAPTER XXVIII. 



REPTILIA. 



(585.) THE globe that we inhabit is usually said to be made up 

 of land and water, and, perhaps, for the purposes of the geogra- 

 pher, such a division of the surface of our planet is all that is 

 requisite. A slight investigation of this subject, however, is 

 sufficient to convince the naturalist, that a very considerable pro- 

 portion of the world around us can scarcely be strictly referred to 

 either one or the other of the geographical sections referred to ; 

 that there are extensive marshes, for instance, equally ill-adapted to 

 be the habitation of aquatic animals, or of creatures organized for a 

 purely terrestrial existence ; that some localities may be alternately 

 deluged with water and parched with drought ; that the margins of 

 our lakes, the banks of our rivers, and the shallow ponds and stream- 

 lets of warm climates, could only be adequately populated by beings 

 of an amphibious character, alike capable of living in an aquatic or 

 in an aerial medium, and combining in their structure the condi- 

 tions necessary for enabling them to reside in either element. 



Aquatic animals, strictly so called, breathe by means of gills ; 

 for a vertebrate animal to respire air, it must be provided with lungs : 

 but if a creature is destined to live both in air and water, it must 

 obviously have both gills and lungs coexistent, either of which may 

 be employed in conformity with the changing necessities and altered 

 circumstances. We cannot, therefore, be surprised to find that in 

 the lowest Reptiles this is literally the arrangement adopted ; that 

 they respire like fishes by means of branchiae while in the water, 

 whereas on emerging into the air they have lungs ready for use. 



(586.) The AMPHIBIA (Batrachia Cuv.) are to the anatomist 

 amongst the most interesting animals in the whole range of zoo- 

 logy, as we trust will be made sufficiently evident when we come to 

 investigate their internal economy ; but it is to their outward 

 forms and habits that we must first introduce the reader, leaving the 

 details of their organization to be discussed in the sequel. 



From whatever form or race of animals the zoologist advances 



