RESEMBLANCES AMONG ANIMALS 47 
a majority of the most eminent living men of science. 
New facts, new problems, new difficulties as they 
arise are accepted, solved or removed by this theory ; 
and its principles are illustrated by the progress and 
conclusions of every well established branch of human 
knowledge. It is the object of the present essay to 
show how it has recently been applied to connect to- 
gether and explain a variety of curious facts which 
had long been considered as inexplicable anomalies. 
Importance of the Principle of Utility. 
Perphaps no principle has ever been announced 
so fertile in results as that which Mr. Darwin so 
earnestly impresses upon us, and which is indeed a 
necessary deduction from the theory of Natural Se- 
lection, namely—that none of the definite facts of 
organic nature, no special organ, no characteristic 
form or marking, no peculiarities of instinct or of 
habit, no relations between species or between groups 
of species—can exist, but which must now be or 
once have been useful to the individuals or the races 
which possess them. This great principle gives us a 
clue which we can follow out in the study of many 
recondite phenomena, and leads us to seek a mean- 
ing and a purpose of some definite character in 
minutiz which we should be otherwise almost sure 
to pass over as insignificant or unimportant. 
Popular Theories of Colour in Animals. 
The adaptation of the external colouring of animals 
