Two irregular forms call for a word of remark. The first is _Chætonotus_ (Plate XIII. Fig. 27), which stands on the borderland of the Infusoria and the Rotifers, neglected as a rule by the students of both; and the second the _Tardigrada_ (Plate XIV. Fig. 21), or water-bears, which have feet like those of the red wriggling larva of _Chironomus_, whose silky tubes are common enough on submerged walls and on the stems of plants, these feet consisting of a mass of radially arranged hooklets, which can be protruded or withdrawn at will; whilst the head of the water-bear is far more like that of a louse, pointed and hard, and suited for burrowing about, as the animal does, among the rubbish at the bottom of the bottle. Both the genera just referred to will repay careful study, as little is known of their life-history or development. A few words must be devoted, in conclusion, to the Entomostraca, those shrimp-like animals which, like their marine relatives, act as scavengers to the community. Fig. 22 is a portrait of _Cypris_, a not very handsome form, but one very commonly found. Its shell is opaque, so that the internal organs are difficult to observe. Far different in this respect is the beautiful _Daphnia_, the water-flea _par excellence_, whose carapace is of crystalline clearness, so that every movement of every one of the internal organs may be followed with the greatest facility. There are many species of the genus, and some of them are very common, so that the opportunity of examining these lovely objects is easily obtained. Plate XIV. Fig. 23, shows the most common of all the class under notice, the _Cyclops_, so named from the fact that, like the fabled giants of classical literature, it has a single eye in the middle of its forehead. It is often loaded with Infusoria, especially Vorticella and Epistylis, already described, to such an extent that its movements are greatly hampered. XII. FIG. 1. Tubercle, Sun-star 2. Zoophyte, Gemellaria 3. Cuttle bone 4. Plate of ditto from above 5. Zoophyte, Antennularia 6. Pedicellaria, skin of Starfish 7. Shell, Foraminifer 8. Snake-star, disc from below 9. Pedicellaria, Echinus 10. Wing-case, Weevil 11. Coralline 12. Spine, Echinus 13. Foraminifer, Polystomella 14. Do. Truncatulina 15. Do. Polymorphina 16. Do. Miliolina 17. Gold dust, with quartz 18. Foraminifer, Lagena vulgaris 19. Pouches, Skin of Rat’s tail 20. Foraminifer, Biloculina ringens 21. Ore, Copper 22. Zoophyte, Membranipora pilosa 23. Human skin, injected 24. Coal, Longitudinal section 25. Do. Transverse section 26. Lung, Frog [Illustration: XII.]