16 INTRODUCTIO.V. 



Musk-rat, the American Buffalo, Tree-Porcupines, and the Turkey. 

 The Beaver, Reindeer (Caribou), Slieep, and Bears are types com- 

 mon to this and the Palaaarctic Region. 



VI. The Xeotrojniyd Province, including the whole of South 

 America, Central America, and Southern Mexico, together with 

 the Antilles. C^haracteristic animals are the Platyrhine Monkeys, 

 Llamas, Peccaries, C'avies, Sloths, Ant-eaters, Armadillos, Trogons, 

 and Curassows. There is an absence of Insectivorous Mammals, 

 (ioats, Antelojies, Oxen, Cranes, &c. The Opossums are common 

 to this and to the Nearctic Province. 



Leaving the dry land, we find that even in the ocean animals are 

 not distributed at random, but have, on the contrary, a more or less 

 definite range. Without entering at length into this very inter- 

 esting subject, two or three of the more important facts connected 

 with the distribution of marine life maj' be stated here. In the 

 first place, certain marine animals affect that portion of the sea- 

 shore wliich lies between tide-marks, and is therefore more or less 

 completely uncovered twice a -day by the retirement of the tide. 

 Technicidly, naturalists call the tract between tide-marks the " Lit- 

 toral Zone " (Latin, litua, the shore). In the second place, we find 

 other animals which do not like to be uncovered by the retiring 

 tide, and which live, therefore, just below the limit of low water, and 

 usually extend their range till the sea becomes about fifteen fathoms 

 in depth. Within these limits the great Tangle {Lam innriri) flourishes 

 in profusion, and hence this is called the " Laminarian Zone." Be- 

 yond the Laminarian Zone are other regions of different depths, 

 which can usually be recognised more or less distinctly by the 

 animals which inhabit them. Finally, by the researches of Car- 

 penter, Wyville Thomson, (iwyn JefiVeys, Wallich, Sars, Pourtales, 

 Agassiz, and other observers, we know that the "deep sea" prop- 

 erly So called, extending fnim a de]5th of .300 fathoms up to at least 

 .3000 or 4000 fathoms, is tenanted by a vast number of animals, 

 constituting a very remarkable and peculiar life-assemblage. We 

 also know now, that, except in very limited depths, the distribution 

 of marine animals is conditioned not by the depth of the water, but 

 by its temperiitiire. Similar forms of marine life are therefore found 

 inhabiting areas in which the bottom temperature is the same, irre- 

 spective of what the depth of the water may be. And it may happen 

 that two neighbouring areas of the sea-bottom may be inhabited 

 by different assemblages of animals, in spite of their being close 

 together, provided one area is swept by a current of warm water, 

 whilst the other has its temjierature lowered by the influx of a cold 

 cm-rent. 



Distribution ix Time. — The distribution of animals in past 



