1.--Ophiodendrum abietinum on Sertularia abietina 66 2.--Ricinus of the Pygarg 72 3.--Caligulus elegans, female: ditto, natural size 73 4.--Different forms of the Bite of a Leech 110 5.--Sucker and jaws 110 6.--Anatomy of Leech 110 7.--Antenna of Gnat 115 8.--Gnat, male and female 118 9, 10.--Lucilia hominivora 120 11.--Ox-fly 121 12.--Antenna of Ox-fly 121 13.--Blue-fly 121 14.--Flesh-fly 122 15.--House-fly 122 16.--Bed-bug 124 17.--Louse 125 18.--Louse--Suckers 126 19.--Ditto--Claw 126 20.--Flea (Pulex irritans) 128 21.--Itch-mite 131 22.--Ditto, female--back view 131 23.--Ditto, male--back view 132 24.--Geographical water-mite 136 25.--Book-mite 137 26.--Chigoe, male 141 27.--Ditto, head 141 28.--Ditto, female 141 29.--Phryxus Rathkei 145 30.--Tracheliastes of Cyprinidæ 149 xi 31.--Lernea branchialis attached to Morrhua luscus 151 32.--Young Guinea-worm, showing Mouth, Tail, and section of Body 153 33.--Gregarinæ of Nemertes 160 34.--Sac with Psorospermiæ from Sepia officinalis 160 35.--Stylorhynchus Melophagus oligacanthus from Dragon-fly 161 36.--Horse-fly, showing also Anterior and Posterior Extremity 172 37.--Macaco Worm 175 38.--Melophagus of the Sheep 177 39.--Lipoptena of Stag 177 40.--Gordius aquaticus 178 41.--Monostomum verrucosum--Sporocyst with Cercariæ 191 42.--Liver fluke 198 43.--Monostomum mutabile 202