NATURAL SELECTION. 
159 
lions of years would have passed away in the formation of 
the Aqueous Rocks. 5o that, while admitting the loose- 
ness of the data, we feel that we are less likely to err in 
assuming an amount of time practically unlimited for the 
development of life than if we attempt to fix a definite 
limit. It is often asked, How could the instincts of animals 
and man arise through a process like Natural Selection? 
The manner in which the young uneducated Pointer ac- 
quired the instinct of pointing explains the origin of all 
instincts. The original Pointer was taught to point, and 
in the course of generations, this peculiarity being inherited, 
the pointing became instinctive. All of our ideas have 
arisen in the same way, mind being the impressions of the 
brain derived from the external world through the medium 
of the senses. Ifthere really be what metaphysicians call 
“a priori ideas," originally they have been derived a pos- 
teriori ; that is, these ideas were originally derived by the 
parent organism, and later inherited by posterity. Finally, 
to many persons, complex structures like the eye and ear 
are insuperable objections to the theory of Natural Selec- 
tion, it seeming incredible to those who are unacquainted 
with Comparative Anatomy that such organs could have 
arisen through the Survival of the Fittest caused by the 
action of a blind, objectless, working Nature. The eye is 
usually studied in a most developed state, as in man, for 
example; but the visual organ of some of the lower animals 
is only a pigment spot, more or less sensitive to the rays 
of light, but incapable of forming the image of an external 
object. As we ascend in the scale of life, we notice there 
is added to this pigment spot a sensitive nerve, and as we 
gradually progress there appears the lens, a light-refracting 
organ, which, collecting the rays of light in a focus, deline- 
ates the image of an external object. Still more highly 
organized animals exhibit additional media of service in 
transmitting the light, a complex retina for receiving the 
