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.