To admit all this is, as it seems to me, to enter into the realms of miracle, and to leave those of science.

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.