hinges of, 154.

littoral, seldom embedded, 270.
fresh-water, long retain the

same forms, 308.

fresh-water, dispersal of, 344.
of Madeira, 349.

land, distribution of, 349.
land, resisting salt water, 325.
Shrew-mouse, 373.
Silene, infertility of crosses, 243.
Silliman, Prof., on blind rat, 110.
Sirenia, their affinities, 302.
Sitaris, metamorphosis of, 394.
Skulls of young mammals, 159, 384.
Slave-making instinct, 216.
Smith, Col. Hamilton, on striped
horses, 129.

Mr. Fred., on slave-making
ants, 217.

-, on neuter ants, 231.
Smitt, Dr., on the Polyzoa, 193.

successively appearing, 290.

changing simultaneously

throughout the world, 297.
Spencer, Lord, on increase in size of
cattle, 26.

Herbert, Mr., on the first steps
in differentiation, 100.

-, on the tendency to an equili-
brium in all forces, 252.

Sphex, parasitic, 216.

Spiders, development of, 390.

Sports in plants, 8.

Sprengel, C. C., on crossing, 76.
-, on ray-florets, 116.
Squalodon, 302.

Squirrels, gradations in structure,

139.

4.

Valenciennes, on fresh-water fish, 344.
Variability of mongrels and hybrids,
259.

Variation under domestication, 5.

caused by reproductive system
being affected by conditions of
life, 7.

under nature, 33.
laws of, 106.

correlated, 9, 114, 159.

Variations appear at corresponding
ages, 10, 67.

124.

analogous in distinct species,

Varieties, natural, 32.

-, struggle between, 59.
domestic, extinction of, 86.
transitional, rarity of, 134.
when crossed, fertile, 257.
when crossed, sterile, 256.
classification of, 371.
Verbascum, sterility of, 238.

varieties of, crossed, 258.
Verlot, M., on double stocks, 230.
Verneuil, M. de, on the succession of
species, 299.

Vibracula of the Polyzoa, 193.

Viola, small imperfect flowers of, 173.
tricolor, 57.

Virchow, on the structure of the
crystalline lens, 145.
Virginia, pigs of, 66.

Volcanic islands, denudation of, 268.
Vulture, naked skin on head, 158.

Wallace, Mr., on the walking-stick
insect, 182.

-, on laws of geographical distri
bution, 322.

on the Malay Archipelago, 351.
on mimetic animals, 377.
Walsh, Mr. B. D., on phytophagic
forms, 38.

-, on equable variability, 125.
Water, fresh, productions of, 343.
Water-hen, 143.

Waterhouse, Mr., on Australian mar-
supials, 90.

on greatly developed parts

being variable, 119.

on the cells of bees, 220.

on general affinities, 379.

Water-ouzel, 142.

Watson, Mr. H. C., on range of va
rieties of British plants, 37, 46.

on acclimatisation, 112.

-, on flora of Azores, 328.
on Alpine plants, 331.

on rarity of intermediate va-
rieties, 136.

on convergence, 100.

on the indefinite multiplication
of species, 101.

Weale, Mr., on locusts transporting
seeds, 327.

Web of feet in water-birds, 142.
Weismann, Prof., on the causes of
variability, 6.

on rudimentary organs, 400.
West Indian Islands, mammals of,
352.

Westwood, on species in large genera
being closely allied to others, 45.
-, on the tarsi of Engidæ, 124.
on the antennæ of hymeno-
pterous insects, 366.

Whales, 182.