Ostracoda, 38; development, 81; luminosity, 127, 151; plankton, 144; fresh-water, 172; of Tanganyika, 184; fossil, 261 Ovary of Lobster, 27 Oxyrhyncha, 64; masking habits, 96; fossil, 270 Oxystomata, 63; habits, 101; protective resemblance, 109; deep-sea, 128; fossil, 269 _Oxyuropoda_, 266 Oyster Crab, 249 Oysters and Pea Crab, 217 Paguridea, 61 _Paguropsis_ and Sea-anemones, 214 _Palæmon_, 179; used for food, 248 _Palæmonetes_, 174 Palinura, 59 Palinuridæ, 241; fossil, 269 _Palinurus_, larva of, 72; fishery, 240 Palp, 14 _Pandalus_, 59, 137; used for food, 245 _Panulirus_, 241 _Paracyamus_, 55 _Paranaspides_, 264 _Paranephrops_, 177 _Parapagurus_, 124; and Sea-anemones, 213 Parasitism, 208 Parastacidæ, 176 _Parastacus_, 178 Partan, 248 Parthenogenesis, 163; of Cladocera, 166; of Ostracoda, 172 Pea Crab, 217 Pedunculata, 43 _Peltogaster_, 232 Penæidea, 59; fossil, 267 _Penæus_, 59; larvæ, 73; used for food, 247; fossil, 268 Peracarida, 46; development, 78 Pericardium, 17 _Peripatus_, tracheæ of, 204 Peter's stone, 220 _Philomedes_, 38 Phosphorescence. See Luminosity Photophores of Euphausiacea, 125 Phreatoicidea, 173 _Phronima_, 154 Phronimidæ, eyes of, 154 _Phtisica_, 54 Phyllocarida, 261 _Phyllosoma_, 149; of Spiny Lobster, 72 Phylogeny, 205, 256 Pill Millipede, 203 Pink Shrimp, 137, 245 _Pinnaxodes_, 218 _Pinnotheres_, 217; used for food, 249 _Planes_, 155 Plankton, 139; of fresh water, 160; of lakes, 168, 170; relation to fisheries, 250 _Platyarthrus_, 205 _Platycuma_, 129 _Platymaia_, 130 _Platytelphusa_, 184 Pleuron, 9 Podocopa, 39 _Podocrates_, 269 _Pollicipes_ used for food, 237; fossil, 261 _Polycheles_, 133 _Pontonia_, 218 _Pontoporeia_, 181 Porcelain Crab: zoëa of, 70; autotomy, 114; feeding, 115; and Hermit Crabs, 215 _Porcellana_: zoëa of, 70; autotomy, 114; feeding, 116 Porcellanidæ, 60 _Porcellio_, 51; structure and habits, 202; distribution, 206 Portunidæ: swimming, 90; sand-burrowing, 99; used for food, 249 Potamobiidæ, 176 Potamobius, 174 _Potamon_, 180; young of, 78 _Præanaspides_, 265 Prawns, 58; luminosity of, 127; of deep sea, 136; of fresh water, 174, 179; of Tanganyika, 183; blind, in caves, 185; in Sponges, 210; Isopods parasitic on, 221; Common, 245; used for food, 245; deep-water, 247; fossil, 268 Prosoponidæ, 135, 269 Protandrous hermaphroditism, 221 Protective resemblance, 108 _Protocarcinus_, 269 _Protocaris_, 260 Protopodite, 10 Protozoëa of _Penæus_, 75 _Psathyrocaris_, 130 _Pseudothelphusa_, 193 Pseudo-tracheæ, 202 Pygidium, 259 _Pygocephalus_, 263