The second is, that the most scrupulous cleanliness will hardly suffice to prevent contamination of preparation by the all-pervasive dust which, invisible to the eye, assumes colossal proportions under the microscope, and the particles of which have an unpleasant habit of collecting on the most interesting or most beautiful portion of the preparation. This can only be guarded against by careful filtration of all fluids, and constant watchfulness. A preparation properly made is a thing of beauty, and a joy for ever,--or if not for ever, at any rate for many years; and one such will repay an infinitude of pains taken in its production. INDEX PAGE Air-pump, 174 Algæ, 78 " marine, 92 Anemones, sea, 159 Antennæ, 96 Ants, 97 Bacillaria, 87 Balancers of Fly, 112 Bark, 61 Blights, 89 Blood, circulation of, 129 " corpuscles of, 128 Bone, 123 Breathing-tubes, 109 Bull’s-eye, use of, 32 Camera lucida, 25 Canada Balsam, 170 Cartilage, 124 Cells, animal, 122 " circulation in, 40 " mounting dry in, 173 " pigment, 121, 165 " spiral, 46 " vegetable, 37 Ceramidia, 93 Chlorophyll, 40 Compressorium, Beck’s, 18 Condenser, bull’s-eye, 19 " substage, 19 Confervæ, 84 Conjugation, 82, 84 Convex lenses, 7 " foci of, 7, 8 " image formed by, 10 " virtual image, 11 Corallines, 164 Corrosive sublimate, 170 Cover-glasses, 18 Desmids, 81 Diatoms, 85 " preparation of, 175 Dipping-tubes, 22 Dissection, 20 " instruments, 21 " under microscope, 24 Drawing, 25 " squares, 26 Echinoderms, 162 Entomostraca, 152 Epidermis, animal, 122 " vegetable, 68 Extemporised apparatus, 5 Feathers, 119 Fish, scales of, 118 " parasites of, 153 Fixation of cell-forms, 171 Focus of mirror, 29 Foraminifera, 156 Formalin, 164 Frog-plate, 129 Gills of mussel, 122 Gizzard of insects, 109 Glycerine-gelatine, 172 " jelly, 171 Hairs, animal, 116 " vegetable, 53 Heads of Insects, 104 Illumination, correct, 31, 32 " dark-field, 34 " for opaque objects, 33 Imbedding, 180 " by infiltration, 182 Infusoria, 135 Injection, 164 Insects, 97 " mounting of, 177 Jelly-fish, 158 Larva of _Chironomus_, 152 Light, arrangement of, 29 Live-box, 17 Logwood solution, 183 Magnification, to measure, 27 Mare’s tail, 91 Marine life, 155 Microscope, Baker’s, 14 " " “portable”, 15 " primitive, 5 " simple, 12, 13 Mildew, 89 Mirror, concave, 29 Mollusca, 161 Mounting, 168 " dry, 173 " foraminifera, 157 Mosses, 96 Muscle, 127 Nails, 124 Needles, 22 Nerve, 127 Net, 133 Nucleus, 40