Apart from these variations in the size of the brain, the characters of
the skull vary. Thus if I draw the figures of a Mongul and of a Negro
head on the blackboard, in the case of the last the breadth would be
about seven-tenths, and in the other it would be nine-tenths of the
total length. So that you see there is abundant evidence of variation
among men in their natural condition. And if you turn to other animals
there is just the same thing. The fox, for example, which has a very
large geographical distribution all over Europe, and parts of Asia, and
on the American Continent, varies greatly. There are mostly large
foxes in the North, and smaller ones in the South. In Germany alone,
the foresters reckon some eight different sorts.

Of the tiger, no one supposes that there is more than one species; they
extend from the hottest parts of Bengal, into the dry, cold, bitter
steppes of Siberia, into a latitude of 50 degrees,--so that they may
even prey upon the reindeer. These tigers have exceedingly different
characteristics, but still they all keep their general features, so that
there is no doubt as to their being tigers. The Siberian tiger has a
thick fur, a small mane, and a longitudinal stripe down the back, while
the tigers of Java and Sumatra differ in many important respects from
the tigers of Northern Asia. So lions vary; so birds vary; and so, if
you go further back and lower down in creation, you find that fishes
vary. In different streams, in the same country even, you will find
the trout to be quite different to each other and easily recognisable by
those who fish in the particular streams. There is the same
differences in leeches; leech collectors can easily point out to you
the differences and the peculiarities which you yourself would probably
pass by; so with fresh-water mussels; so, in fact, with every animal
you can mention.