INTRODUCTION. 
5 
* Origin of Species’ (first edition, p. 199) I contented 
myself by merely alluding to this belief. When I came 
to apply this view to man, I found it indispensable to 
treat the whole subject in full detail. 2 Consequently 
the second part of the present work, treating of sexual 
.selection, has extended to an inordinate length, com- 
pared with the first part ; but this could not be 
.avoided. 
I had intended adding to the present volumes an 
.essay on the expression of the various emotions by man 
and the lower animals. My attention was called to this 
.subject many years ago by Sir Charles Bell’s admirable 
work. This illustrious anatomist maintains that man 
is endowed with certain muscles solely for the sake 
of expressing his emotions. As this view is obviously 
^opposed to the belief that man is descended from some 
•other and lower form, it was necessary for me to consider 
it. I likewise wished to ascertain how far the emotions 
-are expressed in the same manner by the different races 
of man. But owing to the length of the present work, 
I have thought it better to reserve my essay, which is 
partially completed, for separate publication. 
2 Prof. Hackel is the sole author who, since the publication of the 
Origin/ has discussed, in his various works, in a very able manner, 
.the subject of sexual selection, and has seen its full importance. 
