IV. PISCES, or FISHES. SELACHIA (Cartilaginous)—Chimæra, Sharks, Sawfish, Rays. GANOIDEA (Enamel-scales)-Amia, Bony-pike, Sturgeon. TELEOSTIA (Perfect-bones)-Eels, Salmon, Herring, Cod, Pike, &c. INVERTEBRATA, Or animals void of back-bone and bony skeleton, and comprehending ARTICULATA, MOLLUSCA, RADIATA, and PROTOZOA. I. ARTICULATA, subdivided into Articulates and Vermes. 1. ARTICULATA, or Jointed Animals Proper. INSECTA (Insects)-Beetles, Butterflies, Flies, Bees. CRUSTACEA (Crust-clad)—Crayfish, Crabs, Shrimps, Woodlice. 2. VERMES, or Worms Proper. ANNELIDA (Small-rings)-Lobworm, and almost all the marine worms. GEPHYRIA (Intermediates—urchin-like)—Sipunculus, Echinurus. HIRUDINEI (Leeches)- Leeches, Branchellion. TURBELLARIA (Turbellaries)—– Planaria, Ribbon-worms. HELMINTHES (Gut-worms)-Intestinal worms. II. MOLLUSCA, subdivided into Mollusca and Molluscoida. 1. MOLLUSCA, or Shell-fish Proper. CEPHALOPODA (Head-footed)-Cuttle-fish, Octopus, Calamary, Nautilus. GASTEROPODA (Belly-footed)—Snails, Slugs, Whelks, Cowries. 2. MOLLUSCOIDA, or Mollusc-like Animals. TUNICATA (Coated, but Shell-less)— { POLYZOA (Compound animals) or BRYOZOA (Moss-like animals) Biphora, Simple and Compound Flustra, Eschara, Plumatella, &c. III. RADIATA, or ZOOPHYTES-Ray-like Animals. ECHINODERMATA (Urchin-skinned)-Sea-urchins, Star-fishes. ACALEPHE (Sea-nettles)—Jelly-fish, Beroës. POLYPI (Many-feet)-Coral animals, Sea-anemones, Hydras. IV. PROTOZOA, or LOWEST-LIFE-Globular Animals. INFUSORIA (Infusories)—Monads, Volvoces, Vorticella. PORIFERA (Pore-bearers)-Sponges, Fresh-water Sponges. RHIZOPODA (Root-footed)-Amoeba, Polythalamia (Foraminifera). Throwing, as in the case of the vegetable world, these great groups into diagrammatic form, we have first the Protozoan Aspect of Animal Life. Protozoa-the sponges, foraminiferæ, and infusorial animal cules-which, half-plant half-animal, stand, as it were, on the verge of organised existence. Restricted to the waters, rooted as sponges to the sea-bed, appearing as infusoria (we cannot tell how) in stagnant and putrid waters, or thronging in inconceivable numbers as foraminiferæ alike the shallow estuary and the profoundest ocean-depth, their office seems to be the reconversion of organic matter from ultimate decay, and the reconstruction of mineral matter from a state of solution and diffusion. Mere gelatinous specks or glairy films, encased in or encasing some horny, flinty, or limy framework, they constitute the food of many of the lower orders, though their function, on the whole, is mainly formative or geological. As the calcareous muds of existing seas and estuaries are in great part composed of the shelly coverings of the minute foraminiferæ, and the siliceous muds composed of the still minuter shields of infusoria, so we shall afterwards find that extensive strata in the earth's crust owe their formation to similar agencies. Next above these lowest forms of life stand the Radiatathe corals, sea-anemones, jelly-fish, star-fishes, and urchins -all, too, inhabitants of the ocean, and in one or other of their orders appearing in every depth and in every latitude of space. Elaborating from microscopic organisms, the material of their pulpy fabrics, which in turn become the food of the higher orders, their function, though more largely biological than the protozoans, is still in a great measure formative. To coral-zoophytes we owe our existing coral reefs, and from the same source, or from their allies the encrinites, have sprung many of the massive limestones that give character to the crust of the globe. The office of the radiata is thus comparatively humble, as their organisation, though beautifully symmetrical, is simple and lowly. Next we approach the Molluscoida, or mollusclike organisms of modern naturalists-the sea-mats and dead-men's fingers of the fisherman and common observer. Fixed in their habitats, and elaborating, like the corals and sponges, their structures from the waters of the ocean, their functions are humble and their characters obscure. From them we ascend in the zoological scale to the true Mollusca-the oysters, mussels, cockles, whelks, snails, slugs, nautili, and cuttle-fishes-the "shell-fish" of everyday language, though many of them are naked and altogether shell-less. Of more diversified organisation than any of the preceding groups, they are, in one or other of their orders, inhabitants of the ocean, the lake, the river, the marsh, and the dry land. Having also a more cosmopolitan range-feeding, some on plants and others on ani mals-being in turn preyed upon by other races, aquatic, aerial, and terrestrial, and creating extensive calcareous masses with their shelly coverings-the mollusca fulfil im portant vital as well as physical functions. From the enduring nature of their testaceous coverings, they become important indices to the palæontologist, and the interpretations of geology have largely profited by the persistency of their remains. Next in order come the Articulata-the worms, insects, spiders, and crabs-known at once by their many-ringed, segmented, or jointed bodies. Inhabitants of |