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.
Intellectual faculties, their influence on natural selection in man;
probably perfected through natural selection.
Intelligence, Mr. H. Spencer on the dawn of.
Intemperance, no reproach among savages; its destructiveness.
Intoxication in monkeys.
Iphias glaucippe.
Iris, sexual difference in the colour of the, in birds.
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