fclllLOSOl'HV OF ZOOLOGY. 



Well-marked characters. The appetites, so far as we ar 

 able to judge from experience, observation, and analogy, 

 form an essential part of the constitution of every animal. 

 The desires, on the other hand, are not so universally dis- 

 tributed. They constitute rather the distinguishing cha- 

 racters of individuals or species, than of classes, as no one 

 desire (except perhaps that of Warmth) appears common 

 to all. Besides, they^difter from the appetites, in the uni- 

 formity of their excitements. They do not return after cer- 

 tain intervals : and they do not cease to act, upon the at- 

 tainment of their object. 



1. Desire of Warmth. Whether the blood be hot or 

 cold, whether the animal resides on the land or in the 

 waters, there is a particular degree of heat congenial to the 

 feelings, and necessary to the functions of every animal. 

 There is a propensity, in animals at least, to secure this 

 requisite degree of warmth, and its operations, more, per- 

 haps, than any other circumstance, influence their physical 

 distribution. This instinct is destined to guard animals 

 equally against the extremes of heat and cold, and to keep 

 them within that range of temperature most conducive to 

 their health and comfort. In the fixed animals, this defcire, 

 if it exists, cannot excite to action, as locomotion is denied. 



In the execution of its important ends, this instinct 

 guides animals to particular places, to the open sunshine, or 

 the refreshing shade ; to the heated sand-bank, or the cool- 

 ing water; to the exposed mountains, or the sheltered p ] ains. 



The standard of temperature differs according to the 

 species, and even according to the individuals, and the dis- 

 trict of the globe they are destined to dwell in. Hence we 

 find individuals of a species in a variety of situations with 

 regard to temperature, in the same district, and animals 

 thriving in every latitude. 



This desire, like all our powers, is greatly influenced by 



