FACULTIES OF THE MIND. 251 



3. Appetite for Procreation. The two preceding appe- 

 tites are necessary to the existence and well-being of the 

 individual : The one under consideration is subservient to 

 the continuation of the species. As the exercise of the 

 former cannot be dispensed with, in any period, without 

 the decay or death of the individual, they continne to ope- 

 rate from the commencement to the close of life. It is 

 otherwise with the present appetite : for it seldom begins to 

 exert its influence until the body has nearly reached matu- 

 rity, and usually ceases when it is beginning to decay. In 

 many cases, the influence is only felt once during the 

 continuance of life, as in many insects. In other cases, 

 it operates periodically through a considerable portion of 

 life. In all cases, however, it excites to action at such a 

 period, that the young animals to be produced, shall enter 

 life at a season of the year, when temperature, food, and 

 all the other conditions of existence are in the best possible 

 state for their comfort and increase. 



But the most singular property of this instinct, is its se- 

 lective quality, always guiding individuals to those of the 

 same species. Even in the activity of this power, whatever 

 be the age or the season, every animal is indifferent or 

 averse to those of any other species. Hence there is in 

 nature no mixture or contamination of species, every living 

 thing seeking after its kind. 



Domestication produces on this appetite effects equally 

 striking as on the appetite for food. It usually accelerates 

 the period when this power exerts itself, increases the 

 frequency of its demands, and, in a few instances, de- 

 stroys the selective quality. 



II. DESIRES. 



THE instinctive powers which are usually denominated 

 Desires, differ from those of the preceding class in many 



