ROSE DIVISION comprehends four classes of helminthoid animals and the same number of entomoid classes, viz.
6. Entozoa, parasitic, simple, internal, or fixed animals, for the most part of a lengthened cylindrical form, without distinct organs of sense or any internal skeleton, the mouth or anterior part of the body generally provided with recurved sharp spines, the body generally covered with an elastic white transparent inte gument, the nervous system seldom distinct, the vascular system without auricle or ven tricle, without respiratory organs, and with the sexes generally separate. (See ENTOZOA.) 7. Rotifera, minute aquatic animals with distinct nervous and muscular systems, provided with eyes, lateral maxillae, a dorsal vessel, an intestine with two apertures, and with vibratile cilia disposed generally in a circular form around the anterior part of the body. They are termed rotifera from the appearance of revolving wheels produced by the rapid move ment of the cilia disposed around the mouth.
One of these minute wheel animalcules, the hydatina senta, is represented highly magnified in fig. 35, where the mouth (a) is surrounded with long vibratile cilia (b b). The cesophaguS (c) leads to a capacious stomach (d), which becomes a narrow intestine below, opening into the cloaca (e), where the genital organs (i, g, g, h,) also terminate. Several ganglia surround the oesophagus, and a dorsal vessel (o o) is seen extending along the middle of the back and sending out regular transverse branches. All the rotifera are free, most are naked, many are sheathed or loricated, they exhibit no branchial or pulmonary organs, they are remarkable for their fertility and their tenacity of life. (See ROTIFERA.) 8. Cirrhopoda, aquatic, articulated, diplo neurose animals, with articulated cirrhi, and branchiae for respiration, body covered with a fleshy mantle, and fixed in a multivalve shell. These animals are all marine, the branchice are fixed to the bases of the articu fated cirrhi, the mouth is provided with man dibles and maxillw, there is a pulsating dorsal vessel, and a double longitudinal knotted sub abdominal nervous chord. The cirrhopoda have been commonly placed among the molluscous classes from the form of their exterior coverings. (See CI Mtn OPODA.) 9. Annelida, with a long cylindrical body generally divided into transverse segments, and covered with a soft skin; the head commonly provided with antennae and numerous simple eyes, and the mouth with maxill? ; the organs of motion in the form of simple setae or cirrhi extending from the sides of the body in a sin gle or double row. The vascular system of the annelida consists of arteries and veins, without a distinct auricle or ventricle, and the blood. is generally of a red colour. The re spiratory organs are generally in form of external branchke, sometimes of internal air-sacs, and the alimentary canal passes straight through the body with two terminal openings, and with numerous lateral caeca developed in its course, as seen in that of the leech, hirudo medicinalis, (fig. 36.) These lateral caeca (b, c, d, e,.f, g, h, i, k, m,) increasing in length and size from before backwards, are often much more lengthened and divided, as in the halithea. Many of the red blooded worms are fixed in cal careous, arenaceous, or other tubes, and many are free and naked. (See AN N ELIDA .) 10. Myriapoda, with a length ened articulated body equally developed throughout ; the head provided with antennae and sim ple eyes ; the segments of the trunk free, without distinction of thorax and abdomen; the segments furnished with one or two pairs of articulated legs adapted for progressive motion on land ; the respiration is aerial, and performed by which ramify from their commencement in stigmata which open along the whole extent of the body. They do not undergo me tarmorphosis, nor possess compound eyes nor wings, and they have always more than six pairs of feet. (See MY RIAPODA.) 11. Insecta, with six articulated legs extend ing from an articulated trunk, which is divided into .a head, thorax, and abdomen; the head is provided with a labium, a labrum, mandibles, and maxillw, with compound and often also with simple eyes, and a pair of antennae and palpi ; the thorax supports the six legs, and commonly one or two pairs of wings, and has attached to it the moveable segments of the abdomen, which embrace the principal organs of digestion, circulation, and generation. The
respiration is effected by tracheae, which form continuous lateral trunks before they ramify through the body. The circulation is aided by a pulsating dorsal vessel provided with nu merous valves, and the alimentary canal is furnished with salivary and hepatic, and often with pancreatic glands. The sexes are sepa rate, and the genital organs, slow in their development, are highly complicated in the perfect state. These animals generally pass through a series of metamorphoses, and throw off their exuvial covering five or six times during their development. This class is the most numerous in the animal kingdom, com prehending about a hundred thousand species. The greater part of their life is spent in the larva state, during which they are generally most voracious, like the young of other classes. • In the adult state the masticating organs and the digestive apparatus vary much according to the kind of food in the different species, as is seen in comparing the alimentary canal of a carnivorous cicindela campestris (fig. 37.) with that of a phytophagous melolontha vulgaris, (fig. 38.) In the carnivorous insect (fig. 37.) the intestine passes nearly straight through the body with few enlargements in its course, and the glandular organs have a simpler struc ture. The oesophagus passes down narrow from the head, and dilates into a wide glandu lar crop (a), which is succeeded by a minute and this is followed by the chylific stomach (b, c) which is covered like the crop with minute glandular cryptw or follicles. At the pyloric extremity of the chylific stomach, the liver, in form of simple biliary ducts, pours its secretion into that cavity by two orifices on each side (d). The short small intestine (e) opens into a wide colon (f), which terminates in the anus (g). In the vegetable-eating. insect, (fig. 38) the alimentary canal is more lengthened, con voluted, and capacious, with more numerous dilatations, and the glandular organs are more developed. The crop (a) of the melolontha is succeeded by a minute rudimentary gizzard, and to this succeeds a long and sacculated glandu lar or chylific stomach, which becomes narrow and convoluted below, and terminates in a small pyloric dilatation, which receives the four terminations of the biliary organs. The succeeding part of the intestine is also con voluted, and has three enlargements in its course to the anus (e). The liver (c c) is here of great magnitude, and has its secreting surface much extended by the development of innumerable minute caeca from its primary ducts. Insects also often present distinct urinary organs, and numerous glands in both sexes connected with the organs of generation. (See INSECTA.) 12. Arachnida, with the head and thorax united, generally four pairs of legs ; with out antenna, or compound eyes, or wings, or metamorphosis ; the trunk divided into a cephalo-thorax and abdomen ; the head is often• provided with two pairs of chiliform manduca tory organs ; the eyes are simple. The respi ration is aerial, sometimes performed by tra cheae, and sometimes by pectinated pulmonary sacs opening on the sides of the abdominal surface of the trunk. In their nervous, res piratory, and circulating systems they indicate a higher grade of development than insects, and like them are generally inhabitants of the land, attaining considerable size and strength, with cunning, cruel, carnivorous habits, and often provided with poisonous instruments. (See ARACHNIDA.) 13. Crustacea, with the head and thorax generally united, two pairs of antenna, two compound eyes, more than four pairs of legs, the respiration effected by gills, and the shell generally hard and calcareous.. These ento moid aquatic animals are generally carnivorous, and have a short and straight alimentary canal. Their circulating system is often aided by a muscular ventricle. The sexes are separate, and the organs of generation are double and symmetrical in both sexes. Their biliary or gans have a conglomerate form, being com posed of minute glandular follicles grouped together into lobules and larger lobes. Some of theseanimals are fixed and parasitic, and breathe by their general exterior surface ; most are free, and respire by means of branchim placed under the sides of the carapace or ex posed on the under-surface of the post-abdomen.