., on sexual selection, 296 (note)

Pieridae, sexual diversity among, 271

Pigeons, varieties of, 89
domestic, derived from wild rock-pigeons, 90
curious correlations in, 140
white eggs of, protective, 213

Pigs, great increase of, in South America and New Zealand, 28

Pikermi, extinct animals of, 377

Pipits as illustrating divergence, 108

Planorbidae, variations of, 44

Plants, the enemies of, 16
variability of, 76
constitutional variation of, 94
colour relations of, 302
true mimicry rare in, 303
exotic rarely naturalised in Europe, 356
dispersal of, 361
northern, in southern hemisphere, 368
identical on summits of remote mountains, 369
progressive development of, 397
geological development of (diagram), 402

Plovers, recognition marks of (figure), 221

Plumes, origin of accessory, 291
muscular relation of ornamental, 292

Poisonous fruits, 307

Porto Santo, rabbits of, 326

Poulton, Mr. E.B., on variable colours of larvae and pupae, 196, 198
on concealments of insects by resemblance to environment, 202
on protective form of Notodonta ziczac, 210
on inedibility of conspicuous larvae, 237

Pouters, 90

Primulaceae, variations of structure in, 79

Problem, the, before Darwin, 6

Problems in variation and heredity, 410

Progression in plants and animals, 395

Protection by terrifying enemies, 209

Protective colouring, variable, 195
of white-headed fruit-pigeon, 200
of African sun-birds, 200
of Kerivoula picta, 201
of sloths, 201
of larva of Sphinx ligustri, 202
of stick and leaf insects, 203
of caterpillars, 203, 205
of butterflies, 206

Ptilopus cinctus, protective colour of, 200

Pugnacity of birds with accessory plumes, 294

=R=

Rabbit, use of white tail of, 218

Rapid increase of plants, 28

Raspail, M., on variability in a grass, 80

Rat, black, spread of, 34

Rattlesnake, use of rattle of, 262

Raven, why black in arctic regions, 191

Reciprocal crosses, 155

Recognition marks of herbivora, 218
of birds, 222
of tropical forest birds, 224
of insects, 226

Reproductive functions, susceptibility of, 153

Reptiles, geological distribution of, 406

Rhinoceroses, evidence of evolution afforded by fossil, 383

Rocks, all stratified formed in shallow water, 344

Rocky Mountains, scarcity of monocotyledons in, 401

Rodents, prevent woody vegetation in the pampas, 23

Romanes, Professor G.J., on usele