REPTILES. " 273 



CHAPTER XXV. 

 ORDER AMPHIBIA.* 



globe that we inhabit is usually said to be made up of 

 JL land and water, and, perhaps, for the purposes of the geo- 

 grapher, such a division is all that is requisite. A little reflection, 

 however, will convince the naturalist that a very considerable 

 portion of the earth around us can scarcely be referred to either 

 of these geographical sections. That there are extensive marshes, 

 for example, equally unfit to be the habitation of aquatic animals 

 as of creatures adapted to a purely terrestrial existence ; that some 

 localities may be alternately deluged with water and parched with 

 drought : thus the margins of our lakes, the banks of our rivers, 

 and the shallow pools and streamlets of warm climates, can only 

 be adequately populated by beings of an amphibious character, 

 alike capable of living in an aquatic or in an aeriform medium, 

 and combining in their structure the conditions necessary for 

 enabling them to reside in either element. 



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

 to adapt a Vertebrate animal to respire air, it must be provided 

 with lungs, consisting of membranous bags, more or less divided 

 internally into numerous cells, into which the blood-vessels spread 

 like an admirable network, fitted for appropriating oxygen from 

 the air of the atmosphere, instead of from water. But if a crea- 

 ture is destined to live both in air and in water, it must obviously 

 be provided with both gills and lungs coexistent, either of which 

 may be employed in conformity with the necessities of the mo- 

 ment. We cannot, therefore, be surprised that, in the lowest Rep- 

 tiles, this is literally the arrangement adopted : that they respire, 

 like fishes, by means of branchiae or gills while in the water, 

 whereas on emerging into the air they have lungs at their disposal. 

 Such, for example, is the case with 



The Mud-Fish (Lepidpsiren t Protopterus J). These animals are met with 

 both in Africa and America ; they are only found in the ditches of the rice- 

 fields, which are for more than half the year under water, while during the 

 other half they are dry. While the tropical rains continue, or as long as the 

 waters prevail, the creature breathes by gills, and lives the life of a fish, which 

 in outward form it much resembles ; but when the water begins to dry up, it 



*a/A0t'j, amphis, both ; jStow, bioo, to live: living in two elements. 



, lepis lepidos, a scale', siren, an animal noticed further on Scaly Siren. 

 , protos, first; Trrepbv, pteron, a icing Q^ fin i.e., with rudimentary fins. 



IS 



