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 
