INTRODUCTION. 59 



dwell in tlie -water, as their natural and only habi- 

 tation ; for although the cetaceous tribes, or whales 

 and porpoises, which, as we have already observed, 

 are not so much fishes as great beasts of the ocean, 

 are constantly in the water, it is only the bulk of 

 their bodies which is so ; a part of the top of their 

 heads being often kept above the surface, or brought 

 there at short intervals for the purpose of respira- 

 tion. The cetaceous animals breathe air like our- 

 selves; which air finds access to their lungs by 

 by means of holes, called spiracles, situated on the 

 the top of their heads — although, in other respects, 

 quite corresponding to the nostrils of other animals. 

 In like manner, many other mammiferous animals, 

 as the various species of seals, — the morse, or sea- 

 horse, — the hippopotamus, — the otters, — and the 

 New Holland Ornithorynchi, with many others, 

 are more frequently in the water than out of 

 it. The same is also the case with many of the 

 wading and diving birds; while, among the rep- 

 tiles, — the turtle, and the crocodiles, &c., make it 

 nearly their sole habitation. Still no one of these 

 animals is competent — for the same reason as 

 prevents the cetacea from so doing — to remain 

 under water beyond a period more or less limited ; 

 and thus the crocodile, which seldom leaves the 

 immense rivers of tropical countries, — subjected by 

 nature to its rule, — remains, in general, floating on 

 the surface of the water like a large piece of timber, 

 maintaining its respiration without impediment, and 

 ready, at the same time, to seize on such hapless 



