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INSTINCT.
Instincts comparable with habits, but different in their origin--Instincts graduated--Aphides and ants--Instincts variable--Domestic instincts, their origin--Natural instincts of the cuckoo, molothrus, ostrich, and parasitic bees--Slave-making ants--Hive-bee, its cell-making instinct--Changes of instinct and structure not necessarily simultaneous--Difficulties of the theory of the Natural Selection of instincts--Neuter or sterile insects--Summary.
Many instincts are so wonderful that their development will probably appear to the reader a difficulty sufficient to overthrow my whole theory.

I may here premise, that I have nothing to do with the origin of the mental powers, any more than I have with that of life itself.

We are concerned only with the diversities of instinct and of the other mental faculties in animals of the same class.
I will not attempt any definition of instinct.

It would be easy to show that several distinct mental actions are commonly embraced by this term; but every one understands what is meant, when it is said that instinct impels the cuckoo to migrate and to lay her eggs in other birds' nests.