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and on the stems of plants, these feet consisting of a mass of radially arranged hooklets, which can be protruded or withdrawn at will; whilst the head of the water-bear is far more like that of a louse, pointed and hard, and suited for burrowing about, as the animal does, among the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 | 14. | Do. Truncatulina |
| 2. | Zoophyte, Gemellaria | 15. | Do. Polymorphina |
| 3. | Cuttle bone | 16. | Do. Miliolina |
| 4. | Plate of ditto from above | 17. | Gold dust, with quartz |
| 5. | Zoophyte, Antennularia | 18. | Foraminifer, Lagena vulgaris |
| 6. | Pedicellaria, skin of Starfish | 19. | Pouches, Skin of Rat’s tail |
| 7. | Shell, Foraminifer | 20. | Foraminifer, Biloculina ringens |
| 8. | Snake-star, disc from below | 21. | Ore, Copper |
| 9. | Pedicellaria, Echinus | 22. | Zoophyte, Membranipora pilosa |
| 10. | Wing-case, Weevil | 23. | Human skin, injected |
| 11. | Coralline | 24. | Coal, Longitudinal section |
| 12. | Spine, Echinus | 25. | Do. Transverse section |
| 13. | Foraminifer, Polystomella | 26. | Lung, Frog |
XII.
We have not space to figure more of these creatures, but other forms will be found not inferior in interest to those mentioned. The most curious of all are those which earn a dishonest and lazy living by attaching themselves to the bodies of other and larger animals, chiefly fish. One of the largest is the Argulus, the bane of aquarium keepers, which is of considerable size, and attacks gold-fish, and in fact almost any fish to which it can obtain access.
The gills of the stickleback will furnish examples of the curious Ergasilus, which consists chiefly of an enormous pair of hooks and two long egg-bags, the latter, in varying form, being carried by many of the Entomostraca.