23. _Pterostichus (Steropus) madidus_; 23 _a_, antenna. 24. Part of leg of _Pterostichus madidus_: _a_, tibia; _b_, tarsus. 25. Labrum of _Pterostichus madidus_. 26. Mandible of _Pterostichus madidus_. 27. Labium of _Pterostichus madidus_: a, mentum; b, labial palp. 28. Maxilla of Pterostichus madidus: _a_, claw; _b_, _c_, maxillary palps. 29. Proboscis of House-fly. 30. Larva of Flea. 31. Larva of _Chironomos plumosus_. 32. Foot of House-fly. 33. Eye of House-fly. 34. Leg of Ant (_Formica fusca_); 34*, pectinate process. [Illustration: Plate X. W Bagg sculp London: John Van Voorst.] _Preparation._--The organs of the mouth, &c., of the Spiders are easily prepared for examination, by carefully pulling them off with forceps or the mounted needles, then drying them under pressure between two glass slips, macerating in turpentine, and mounting in balsam. Those of the Acarina should be dissected out with the needles, after the body has been crushed in a drop of water on a slide, and the internal substance has been gently washed away with a hair pencil. They may then be dried on a slide, with a cover laid on, and turpentine applied to the edge of the cover, balsam being added when most of this has evaporated. The various parts may also be mounted in chloride of calcium or glycerine. INSECTS.--The members of the class of Insects are extremely interesting to the microscopic observer, not only on account of the beautiful structures which they present, but also from these being comparatively large, usually coloured, and easily distinguished under the lower powers. Hence they form admirable objects for study to those who are but little accustomed to the use of the microscope. MYRIAP´ODA (μὑριος, myriad, ποῦς, foot).--This Order contains those insects which are popularly known as the hundred-legs and millepedes; by many zoologists they have been arranged in a distinct class.