1625. Without entering into any detail, in a work like the present, as to the peculiar characters which have led to the establishment of separate orders for the flea, earwig, Thrips, Stylops, and caddice-flies; it will be sufficient for all practical purposes to state that, with these exceptions, all those articulated animals which undergo a system of metamorphosis whereby (in the majority of cases) wings are developed, are divisible into two great groups, namely, those which take their food by means of jaws for mastication, and those which are provided with a suctorial apparatus for pumping up fluid matter for their subsistence. The former primary group (Mandibulata, or insects provided with mandibles or jaws) is divided into the orders, 1. Coleoptera; 2. Orthoptera (including the Euplexoptera and Thysanoptera); 3. Neuroptera (including the Trichoptera); and 4. Hymenoptera. The latter primary group (Haustellata, or insects furnished with a haustellum or sucker) forms the orders, 5. Lepidoptera; 6. Hemiptera; and 7. Diptera (with Aphaniptera and Strepsiptera). The articulated animals, furnished with jointed legs, which do not undergo any metamorphosis whereby wings are developed (A'ptera), now constitute several distinct classes; namely, 1. Crustacea, generally ten-footed, including crabs, lobsters, shrimps, &c.; 2. Arachnida, generally eight-footed, including spiders, scorpions, mites, &c.; 3. Myriapoda, many-footed, including centipedes, millepedes, &c.; 4. Hexapoda, six-footed, including the spring-tailed insects and lice.