by incurrent pores.

Class PORIFERA. Equivalent to the Phylum. Subclass 1. Calcarea. Sponges with skeleton of calcareous spicules.

Subclass 2. Non-Calcarea. Skeleton, when present, composed of siliceous spicules or of spongin fibres. Phylum III. COELENTERATA (Polyps, etc.). Animals of radial structure, whose digestive

cavity is lined by the body-wall, and which have nettling organs. Class 1. HYDROZOA. Colenterates, whose body is composed of more than two rays, and contains a single cavity (Hydroids, Siphonophores, etc.).

Class 2. SCYPHOZOA. Cœlenterates with many radii, and with radial partitions in the cavity of the body (Jellyfishes).

Class 3. ACTINOZOA. Attached individuals or colonies.

Subclass 1. Zoantharia. Tentacles numerous, and usually in multiples of five (Sea-Anemones, Madrepores, and Corals).

Subclass 2. Alcyonaria. Tentacles, eight only (Red Corals, Sea-Fans, etc.). Class 4. CTENOPHORA. Colenterates with only two radii, and rows of ciliaplates.

Phylum IV. PLATYHELMINTHES (Flatworms). Bilaterally symmetrical, soft-bodied animals, without true segmentation of the body; flattened in a dorso-ventral direction, and having the bodycavity filled with a loose meshwork of cells. Class 1.

TURBELLARIA. Free-living flatworms, whose body is covered by cilia; alimentary tract with only opening to the exterior (Planarians).

one

Class 2. TREMATODA. Parasitic,

unsegmented, without cilia in the adult, and with a well-developed digestive apparatus (Flukes).

Class 3. CESTODA. Elongated, usually unsegmented hermaphrodite endoparasites, without mouth or alimentary canal (Tapeworms, etc.).

malcules.) Characterized by having the larva in

the form of a trochosphere.

Class 1.

ROTIFERA.

Microscopic wheelanimalcules, with a ciliated band around the mouth, and a special organ for attachment.

Class 2. DINOPHILEA. Minute, worm-like, having five to eight segments, usually ciliated; and nephridia in pairs; marine.

Class 3. GASTROTRICHA.

Minute, spindleshaped, flattened and ciliated on the ventral surface; fresh waters. Phylum VII. MOLLUSCOIDA (Sea-Mats and

Brachiopods). Small aquatic animals, having a true body-cavity (except in Endoprocta) and suspended alimentary canal; dorsal region abbreviated and surmounted by lophophore.

Class 1. POLYZOA. Molluscoida that form colonies connected by one organic substance; the ciliated band of the lophophore is drawn out into tentacles (Bryozoans).

Subclass 1. Ectoprocta. Anus outside tentacular corona.

Subclass 2. Endoprocta. Anus internal; form colonies by budding.

Class 2. PHORONIDA. Worm-like polyzoans, living in associations of individuals born from ova, not by buds. Class 3. BRACHIOPODA. Polyzoa with the body inclosed in a shell of two valves; body usually attached by a stalk (Lamp-Shells). Phylum VIII. ECHINODERMATA (Echinodermis). Animals of prevailingly radical structure, with intestinal wall distinct from body-wall, and with calcareous plates in the skin. Class 1.

ASTEROIDEA. Star-shaped echino-
derms, with a furrow (ambula-
crum) along the under side of the
arms (Starfish).

Class 2. OPHIUROIDEA. Star-shaped echino-
derms, with the arms sharply
marked off from the body, and
not grooved (Brittle Stars).
Class 3. ECHINOIDEA. Echinoderms with
the body globular or disk-shaped,
and armless (Sea-Urchins).

Class 4. HOLOTHUROIDEA. Echinoderms
elongated, worm-like, usually soft,
and with tentacles about the
mouth (Trepangs).

Class 3.

Class 2. TRILOBITA. Body depressed, oval, and divided into head, thorax, and abdomen (Extinct Trilobites). ONYCHOPHORA. Cylindrical, unsegmented, papillose, and with a series of short walking appendages (Peripatus).

Class 4. MYRIAPODA. Tracheate arthropods, consisting of several segments, each bearing one or two pairs of legs (Centipedes and Millipedes). Class 5. INSECTA. Arthropods with the body in three divisions-head, thorax, and abdomen-with six thoracic legs, and usually with wings (Insects).

ar

Class 6. ARACHNIDA. Air-breathing thropods, without antenna (Spiders, Scorpions, etc.).

Ani

Phylum XI. MOLLUSCA (Mollusks). mals with unsegmented body, and without jointed appendages; usually with a shell, and with a muscular organ of locomotion (the foot).

NOTE. The Pycnogonida, Linguatulida, and Tardigrada, "though not in any way related to one another, and of doubtful relationships to the Arachnida, are, as a matter of convenience, mentioned together here."-Parker and Haswell.

а

Class 1. PELECYPODA. Mollusks with nearly symmetrical body, leaflike gills, and a two-valved shell (Bivalves). Bilaterally sym

Class 2. AMPHINEURA.

metrical; anus at end of body (Chitons).

Class 3. GASTROPODA. Body unsymmetrical, with head, feelers, eyes, and unpaired foot; shell (when present) univalve (Gastropods).

Subclass 1. Streptoneura. Visceral commissures twisted into a figureof-8; sexes distinct (Limpets, Whelks, etc.).

Subclass 2. Euthyneura. Visceral commissures not twisted into a figure-of-8; sexes united (Pulmonates, Nudibranchs, etc.). SCAPHOPODA. Head rudimentary; mouth-lobes formed into a tube, inclosing the delicate shell (Marine).

Class 4.

Subclass 1. Scaphopoda. As above (Tusk-
Shells).

Subclass 2. Rhodope. Minute, ciliated;
no shell.

Class 5. CEPHALOPODA. Head large; mouth surrounded by arms; foot funnelshaped (Cuttlefish).

Subclass 1. Dibranchiata. Two symmetrical branchiæ; funnel tubular (Squids and Octopods).

Subclass 2. Tetrabranchiata. Four branchiæ; shell multilocular (Nautilus and Ammonites).

Phylum XII. CHORDATA (Chordates). Animals having a notochord, which may (Subphylum C) persist from birth, and become "in the adult replaced more or less completely by a seg mented bony or cartilaginous axis-the spinal

or vertebral column."

Subphylum and Class A. ADELOCHORDA. Marine worm-like animals, having a notochord as larvæ (Balanoglossus, etc.).

Subphylum and

Class B. UROCHORDA. Animals, simple or compound, marine, inclosed in a coriaceous test, composed largely of cellu lose, and having a notochord when larvæ (Ascidians).

Subphylum С. VERTEBRATA. Animals bilaterally symmetrical, and hav ing a backbone (Vertebrates). SEC. I. ACRANIA. Without a head (includes only the family Branchiostomida, Amphioxus, etc.). SEC. II. CRANIATA. With a head (Fishes, Reptiles, Birds, Mammals).

Class 1. CYCLOSTOMATA. Eel-like vertebrates, without a lower jaw; mouth suctorial, and armed with horny teeth (Lampreys). Class 2. PISCES. Aquatic vertebrates, with persistent gills and paired fins (Fishes).

Subclass 1. Elasmobranchii. Fishes with

a cartilaginous skeleton, in which the cranium is never ossified, nor contains membrane-bones; gill openings usually in five pairs (Sharks and Rays).

Subclass 2. Holocephali. Cartilaginous fishes with four pairs of gill-slits, nearly concealed by a old of skin (Chimæras).

Subclass 3. Teleostomi. Fishes with the skeleton complicated by membrane-bones and ossifications, or completely bony (Sturgeons and ordinary Fish). Subclass 4. Dipnoi. Fish-like animals, having an apparatus for breathing atmospheric air (Lungfishes).

Class 3.

Subclass 5. Ostracodermi. Paleozoic fishes, with an exoskeleton extraordinarily developed about the head, and apparently with no endoskeleton (Cephalaspis, etc.). АМРНІВІА. Amphibious vertebrates, breathing by gills in the larval condition, and (usually) by lungs when adult, and having legs and five-toed feet (Amphibians). Class 4. REPTILIA. Elongated, air-breathing vertebrates, with a horny epidermal skeleton of scales and one occipital condyle (Reptiles). Class 5. AVES. Vertebrates clothed with feathers (Birds). Subclass 1. Archæornithes. Birds having a prolonged tail of many vertebræ (Archæopteryx). Subclass 2. Neornithes. Birds having the tail-vertebræ compacted into a pygostyle (Modern Birds). MAMMALIA. Vertebrates which suckle their young, and are more

Class 6.

or less clothed with hair (Mammals).

Subclass 1. Prototheria. Mammals with oviducts separated (Didelphia). Subclass 2. Theria. Mammals with oviducts united for a longer or shorter part of their length (Monodelphia).

A. Metatheria. Young born in rudimentary condition, and sheltered in a pouch (Marsupials).

B. Eutheria. Young born in a uterus; no pouch present (higher Mammals). BIBLIOGRAPHY. In addition to works mentioned above, consult: Bronn (editor), Klassen und Ordnungen des Thierreichs (Leipzig and Heidelberg, 1859, et seq.); Haeckel, Natürliche Schöpfungsgeschichte (Jena, 1868); Lankester, Notes on Embryology and Classification (London, 1877), and article "Zoology" in 9th ed. Encyclopædia Britannica; Leunis, Synopsis der Thierkunde (Hanover, 1883-86); Huxley, Anatomy of Vertebrates (New York, 1878), and Anatomy of Invertebrated Animals (New York, 1888); Standard Natural History (Boston, 1885); Lang, Text-book of Comparative Anatomy (London, 1891-96); Newton, Dictionary of Birds (London and New York, 1893-96); Royal Natural History (London, 1895); Cambridge Natural History (Cambridge, Eng., 1895, et seq.); Parker and Haswell, Text-book of Zoology (London and New York, 1897); Davenport, Introduction to Zoology (New York, 1900). See, also, books mentioned under EVOLUTION; EMBRYOLOGY; and such titles as BIRD, FISH, INSECT, etc., and under biographies of the naturalists above mentioned.

CLASSIFICATION OF SHIPS. See Al; and LLOYDS.