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and

manufactured

instruments,

a perfect

division

of labour

could be

effected

with them

only by

the

workers

being

sterile;

for had

they been

fertile,

they would

have

intercrossed,

and their

instincts

and

structure

would have

become

blended.

And nature

has, as I

believe,

effected

this

admirable

division

of labour

in the

communities

of ants,

by the

means of

natural

selection.

But I am

bound to

confess,

that, with

all my

faith in

this

principle,