as, marine, 348.

Fear, instinctive, in birds, 212.

Feet of birds, young molluscs adhering to, 385.

Fertility:
of hybrids, 249.
from slight changes in conditions, 267.
of crossed varieties, 267.

Fir-trees:
destroyed by cattle, 71.
pollen of, 203.

Fish:
flying, 182.
teleostean, sudden appearance of, 305.
eating seeds, 362, 387.
fresh-water, distribution of, 384.

Fishes:
ganoid, now confined to fresh water, 107.
electric organs of, 192.
ganoid, living in fresh water, 321.
of southern hemisphere, 376.

Flight, powers of, how acquired, 182.

Flowers:
structure of, in relation to crossing, 97.
of compositae and umbelliferae, 144.

Forbes, E.:
on colours of shells, 132.
on abrupt range of shells in depth, 175.
on poorness of palaeontological collections, 287.
on continuous succession of genera, 316.
on continental extensions, 357.
on distribution during glacial period, 366,
on parallelism in time and space, 409.

Forests, changes in, in America, 74.

Formation, Devonian, 334.

Formations:
thickness of, in Britain, 284.
intermittent, 290.

Formica rufescens, 219.

Formica sanguinea, 219.

Formica flava, neuter of, 239.

Frena, ovigerous, of cirripedes, 192.

Fresh-water productions, dispersal of, 383.

Fries on species in large genera being closely allied to other
species, 57.

Frigate-bird, 185.

Frogs on islands, 393.

Fruit-trees:
gradual improvement of, 37.
in United States, 85.
varieties of, acclimatised in United States, 142.

Fuci, crossed, 258.

Fur, thicker in cold climates, 133.

Furze, 439.

Galapagos Archipelago:
birds of, 390.
productions of, 398, 400.

Galeopithecus, 181.

Game, increase of, checked by vermin, 68.

Gartner:
on sterility of hybrids, 247, 255.
on reciprocal crosses, 258.
on crossed maize and verbascum, 270.
on comparison of hybrids and mongrels, 272.

Geese:
fertility when crossed, 253.
upland, 185.

Genealogy important in classification, 425.

Geoffrey St. Hilaire:
on balancement, 147.
on homologous organs, 434.

Geoffrey St. Hilaire, Isidore:
on variability of repeated parts, 149.
on correlation in monstrosities, 11.
on correlation, 144.
on variable parts being often monstrous, 155.

Geographical dist