G70 REPTILIA. 



CHAPTER XXVII. 



EEPTILIA. 



(1857.) THE globe that we inhabit is usually said to be made up of 

 land and water ; and perhaps, for the purposes of the geographer, such a 

 division of the surface of our planet is all that is requisite. A slight in- 

 vestigation of this subject, however, is sufficient to convince the naturalist 

 that a very considerable proportion of the world around us can scarcely be 

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

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

 adapted to be the habitation of aquatic animals and 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 streamlets 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 conditions necessary for 

 enabling them to reside in either element. 



(1858.) 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 ob- 

 viously have both gills and lungs coexistent, either of which may be 

 employed in conformity with the changing necessities and altered cir- 

 cumstances. We therefore cannot 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. 



(1859.) The AMPHIBIA (Batrackia, Cuv.) are to the anatomist amongst 

 the most interesting animals in the whole range of zoology, as we trust 

 will be made sufficiently evident when we come to investigate their in- 

 ternal 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. 



(1860.) From whatever form or race of animals the zoologist advances 

 towards the next succeeding it in the great scale of Nature, he will find 

 himself insensibly led on by such gentle gradations that the transition 

 from any one class to another is almost imperceptible. Nihil per saltum 

 is one of the most obvious laws in creation ; and of this, perhaps, we 

 could not select a more striking illustration than is afforded by the Lepi- 

 dosiren (fig. 328). 



(1861.) Two distinct species of this most remarkable animal have 



