TROPICAL AMERICA. MEXICO. 71 



we may gather from the above facts, that Mexico ex- 

 hibits nearly as great a variety in her animal produc- 

 tions as she does in her vegetable. Both may be traced 

 to the same cause, the astonishing variety of climates 

 concentrated in this isthmus ; where the traveller can 

 pass, in the space of three days, from the regions of 

 perpetual snow, to the burning sands of Vera Cruz. 

 Between these two extremes of heat and cold are stu- 

 pendous ridges or platforms, at different elevations, of 

 table lands ; as if nature, within a single degree of lati- 

 tude, intended to represent the climate, the animals, 

 and the vegetables of every region in the New World. 



(101.) Aquatic birds are generally more nume- 

 rous in cold than in warm latitudes ; yet Mexico 

 is a remarkable and almost a solitary exception. All 

 travellers agree in stating, that the lakes and marshes 

 on the table land are frequented by innumerable water- 

 fowl; their numbers, in fact, are so immense, that 

 they are killed by batteries placed in a double file, 

 and many hundreds are brought down at a single 

 discharge.* Yet among all those which have been 

 sent to England , we only discovered two new bit- 

 terns, the Mexican and the lineated species ; the rest 

 were of ducks and waders, well known in the United 

 States, and nearly all inhabiting the Arctic regions. It 

 would thus appear that the freshwater lakes of the 

 isthmus form the southern barrier of all these migra- 

 tory tribes, no less than of the insectivorous summer 

 visiters of the United States ; since we are,, at present, 

 unacquainted with a single instance of a natatorial bird 

 of North America having been detected on the Terra 

 Firma. Some few of the small sandpipers may, however, 

 occasionally pass to the south of the equinoctial line. 



(102.) The only Mexican reptile deserving particu- 

 lar notice, is the Phytthydrus pisciformis Br. (the 

 Axolotl of Humboldt), allied to the Siren of Carolina. 

 It seems to abound in the lakes near tjie city of 

 Mexico, and is much esteemed as an article of food. 



* Ward's Mexico, 

 F 4 



