Noble, Mr., on fertility of Rhododendron, 251.

Nodules, phosphatic, in azoic rocks, 307,

Oak, varieties of, 50.

Onites apelles, 135.

Orchis, pollen of, 193,

Organs:  of extreme perfection, 186, electric, of fishes, 192. of little importance, 194. homologous, 434. rudiments of, 450.

Ornithorhynchus, 107, 416.

Ostrich:  not capable of flight, 134. habit of laying eggs together, 218.  American, two species of, 349.

Otter, habits of, how acquired, 179.

Ouzel, water, 185.

Owen, Professor:  on birds not flying, 134. on vegetative repetition, 149. on variable length of arms in ourang-outang, 150. on the swim-bladder of fishes, 191. on electric organs, 192. on fossil horse of La Plata, 319. on relations of ruminants and pachyderms, 329. on fossil birds of New Zealand, 339. on succession of types, 339. on affinities of the dugong, 414. on homologous organs, 435. on the metamorphosis of cephalopods and spiders, 442.

Pacific Ocean, faunas of, 348.

Paley on no organ formed to give pain, 201.

Pallas on the fertility of the wild stocks of domestic animals, 253.

Paraguay, cattle destroyed by flies, 72.

Parasites, 217.

Partridge, dirt on feet, 362.

Parts:  greatly developed, variable, 150. degrees of utility of, 201.

Parus major, 183.

Passiflora, 251.

Peaches in United States, 85.

Pear, grafts of, 261.

Pelargonium:  flowers of, 145. sterility of, 251.

Pelvis of women, 144,

Peloria, 145.

Period, glacial, 365.

Petrels, habits of, 184.

Phasianus, fertility of hybrids, 253.

Pheasant, young, wild, 216.

Philippi on tertiary species in Sicily, 312.

Pictet, Professor:  on groups of species suddenly appearing, 302, 305. on rate of organic change, 313. on continuous succession of genera, 316. on close alliance of fossils in consecutive formations, 335. on embryological succession, 338.

Pierce, Mr., on varieties of wolves, 91.

Pigeons:  with feathered feet and skin between toes, 12. breeds described, and origin of, 20. breeds of, how produced, 39, 42. tumbler, not being able to get out of egg, 87. reverting to blue colour, 160. instinct of tumbling, 214. carriers, killed by hawks, 362. young of, 445.

Pistil, rudimentary, 451.

Plants:  poisonous, not affecting certain coloured animals, 12. selection applied to, 32. gradual improvement of, 37. not improved in barbarous countries, 38. destroyed by insects, 67. in midst of range, have to struggle with other plants, 77. nectar of, 92, fleshy, on sea-shores, 132. fresh-water, distribution of, 386. low in scale, widely distributed, 406.

Plumage, laws of change in sexes of birds, 89.

Plums in the United States, 85.