44.--Ditto, ciliated Embryo and young Cercariæ 202 45.--Cercaria of Amphistoma sub-clavatum 203 46.--Sporocyst of Amphistoma sub-clavatum 203 47.--Ditto, from Frog 205 48.--Polystomum integerrimum 205 49.--Cysticercus 206 50.--Vesicular Worm 211 51.--Tape-worm (Tænia solium), showing Scolex and Proglottides 214 52.--Ditto, Rostellum and Suckers 214 53.--Tænia medio-canellata 219 54.--Coenurus of Sheep, and Hydatid 223 55.--Scolex of Tænia echinococcus 226 56.--Tænia echinococcus from the Pig 226 57.--Ditto, from the Dog 227 58.--Bothriocephalus latus 227 59.--Scolex of ditto 227 60.--Egg of ditto 227 61.--Tænia variabilis from Snipe 230 62.--Ditto, more highly magnified 230 63.--Tetrarhynchus appendiculatus from the Plaice 230 64.--Hook of Linguatula 232 65.--Linguatula, showing Hooks 232 66.--Strongylus gigas, female 239 67.--Ascaris lumbricoides; also Head, Tail, and Body 240 68.--Trichocephalus from Man 241 69.--Oxyuris vermicularis, natural size and magnified 241 xii 70.--Trichina, free 243 71.--Trichina encysted in Muscle 243 72.--Echinorhynchus proteus 252 73.--Sac with Psorospermiæ from Sepia officinalis 252 74.--Gregarinæ from Nemertes Gesseriensis 253 75.--Stylorhynchus oligacanthus 253 76.--Dicyema Krohnii from Sepia officinalis 254 77.--Stylops 256 78.--Ditto, with Embryos 257 79.--Larva of Black Stylops 257 80.--Cochineal Insects, male 263 81.--Ditto, female 264 82.--Aphis 264 83.--Rose Aphis, male and female 265 INTRODUCTION. xiii "The edifice of the world is only sustained by the impulses of hunger and love."--SCHILLER.