head, 197.
----, young, wild, 216.
Turnip and cabbage, analogous variations of, 159.
Type, unity of, 206.
Types, succession of, in same areas, 339.

U.

Udders enlarged by use, 11.
----, rudimentary, 451.
Ulex, young leaves of, 439.
Umbelliferae, outer and inner florets of, 144.
Unity of type, 206.
Use, effects of, under domestication, 11.
----, effects of, in a state of nature, 134.
Utility, how far important in the construction of each part, 199.

V.

Valenciennes on fresh-water fish, 384.
Variability of mongrels and hybrids, 274.
Variation under domestication, 7.
---- caused by reproductive system being affected by conditions of life,
8.
---- under nature, 44.
----, laws of, 131.
Variations appear at corresponding ages, 14, 86.
----, analogous in distinct species, 159.
Varieties, natural, 44.
----, struggle between, 75.
----, domestic, extinction of, 111.
----, transitional, rarity of, 172.
----, when crossed, fertile, 268.
----, when crossed, sterile, 269.
----, classification of, 423.
Verbascum, sterility of, 251.
----, varieties of, crossed, 271.
Verneuil, M. de, on the succession of species, 325.
Viola tricolor, 73.
{502}
Volcanic islands, denudation of, 285.
Vulture, naked skin on head, 197.

W.

Wading-birds, 386.
Wallace, Mr., on origin of species, 2.
----, on law of geographical distribution, 355.
----, on the Malay Archipelago, 395.
Wasp, sting of, 202.
Water, fresh, productions of, 383.
Water-hen, 185.
Waterhouse, Mr., on Australian marsupials, 116.
----, on greatly developed parts being variable, 150.
----, on the cells of bees, 225.
----, on general affinities, 429.
Water-ouzel, 185.
Watson, Mr. H. C, on range of varieties of British plants, 58.
----, on acclimatisation, 140.
----, on flora of Azores, 363.
----, on Alpine plants, 368, 376.
----, on rarity of intermediate varieties, 176.
Weald, denudation of, 285.
Web of feet in water-birds, 185.
West Indian islands, mammals of, 396.
Westwood on species in large genera being closely allied to others, 57.
---- on the tarsi of Engidae, 157.
---- on the antennae of hymenopterous insects, 415.
Wheat, varieties of, 113.
White Mountains, flora of, 365.
Wings, reduction of size, 134.
---- of insects homologous with branchiae, 191.
----, rudimentary, in insects, 450.
Wo