Insects, relative size of the cerebral ganglia in; male, appearance of, before the females; pursuit of female, by the males; period of development of sexual characters in; secondary sexual characters of; kept in cages; stridulation.
Insessores, vocal organs of.
Instep, depth of, in soldiers and sailors.
Instinct and intelligence.
Instinct, migratory, vanquishing the maternal.
Instinctive actions, the result of inheritance.
Instinctive impulses, difference of the force; and moral impulses, alliance of.
Instincts, complex origin of, through natural selection; possible origin of some; acquired, of domestic animals; variability of the force of; difference of force between the social and other; utilised for new purposes.
Instrumental music of birds.
Intellect, influence of, in natural selection in civilised society.