-letters to.
-letters to Darwin from.
-on tetrabranchiata.

Hyatt and Cope, theories of.

Hybridism, chapter in "Origin" on.
-Bentham's address on.
-treatment by Darwin in "Variation of Animals and Plants."

Hybrids, and adaptation.
-Darwin's views on.
-evidence in favour of pangenesis from.
-experiments on.
-fertility of.
-intermediate character of.
-primrose and cowslip.
-article in "Quarterly Review" on.
-sterility of.
-Max Wichura on.
-Bronn on.
-F. Muller's work on.
-and heterostyled plants.
-rarity of natural.
-J. Scott's work on.
-tendency to reversion.

Hydra, sexuality of.

Hydropathy, Darwin and.

Hydrozoa, alternation of generations in.

Hymenoptera, affinities of.
-H. Muller on.

Hypericum perforatum, a social plant in U.S.A.

Hyracotherium cuniculus, Owen on.

Iberis, mucus in seeds of.

Ice, as agent in dispersal of boulders.
-agent in dispersal of plants.
-Forbes on transport by.
-agent in lake-formation.
-cleavage in.
-work of, a new factor in geology.

Ice-action, on land and sea.

Icebergs, as factor in explaining European plants in Azores.
-Croll on action of.
-Darwin on.
-evidence in S. America of.
-Hopkins on action of.

Ice-cap, of Arctic regions.

Iceland, importance of records of volcanic phenomena in.

Ignorance, Darwin on immensity of man's.

Ilkley, Darwin's visit to.

Illegitimate offspring, need for repetition of Darwin's experiments on
plants'.

Imatophyllum.

Immortality, Darwin on.

Immutability of species.
-Falconer disbelieves in.
-Darwin on.

Imperfection of the Geological Record, see Geological Record.

Impotence in plants.
-see also Self-sterility.

India, British rule in.
-flora of.
-Hooker in.
-varieties of domestic animals in.
-H.F. Blanford on.
-Darwin on origin of lakes in.
-evidence of colder climate in.
-J. Scott accepts post in.

Infants, Mrs. E Talbot on development of mind in.
-observations on ears of.

Infusoria, possible occurrence in underclays of coal.

Inglis, Sir R., Darwin at breakfast party.

Inheritance, atavism and.
-conservative tendency of long.
-Hackel on.
-hypothesis on.
-Jager on.
-and Natural Selection.
-power of.
-J.C. Prichard on.
-and variability.
-Darwin on.
-Galton on.

Insanity, concealment of.

"Insect Life," Howard's.

Insectivorous plants, Darwin's work on.

Insects, alpine.
-Lord Avebury