188 JOURNAL OF THE PLYMOUTH INSTITUTION. 
of the science which have been hitherto unsuspected are now for 
the first time brought to light. No longer is it enough to say that 
such and such an action on the part of an animal is determined by 
instinct, and as such is beyond the reach of further explanation. 
Now the very thing to be explained is the character and origin of 
the instinct — the causes which led to its development, its con- 
tinuance, its precision, and its use. No longer is it enough to 
consider the interests manifested by one animal as an isolated body 
of phenomena, devoid of any scientific meaning, because thus 
standing out of relation to any known or scientific causes. The 
whole scientific import of instincts as manifested by one animal 
now depends on the degree in which they are connected by general 
principles with the instincts which are manifested by other animals. 
So that just as in the science of comparative anatomy the scientific 
interest which attaches to the study of an animal body depends on 
the relations which the anatomy of the body presents to that of 
other animals, so in the now embryonic science of comparative 
psychology all the phenomena of mind as they occur in one 
animal would be almost destitute of scientific interest, unless they 
admitted of being compared with the phenomena of mind as 
presented by other animals. And. in the one science, as in the 
other, the principle which infuses philosophical life into all these 
comparisons is that which is furnished by the doctrine of evolu- 
tion." 
I have quoted thus largely, because these sentences of Mr. Eomanes 
show what is meant by the study of Comparative Psychology, and 
one which is just now engaging much attention. In his Dublin 
address he goes more fully into the argument. 
He first refers to the principles of human psychology, and shows 
the three stages of perception — " 1st, That of immediate perception; 
2nd, That of ideal representation of particular objects ; and 3rd, 
That of a generalized conception or abstract idea of a number 
of qualities, which a whole class of objects agree in possessing," 
and divides the latter division into two sub-divisions; viz., " abstract 
ideas which are sufficiently simple to be developed without the aid 
of language, and abstract ideas which are so complex as not to 
admit of development without the aid of language." The first is 
illustrated by the necessity for food, which, while quite independent 
of language, is an abstract idea. 
He then points out that all mental processes are accompanied by 
