The animals of this order have generally a lengthened, subprismatic body, covered with a highly irritable elastic and coreaceous integument. The mouth and anus are distinct, and placed at the opposite extremities of the body. The mouth is often surrounded with numerous extended ramified tentacula capable of retraction. The respiratory organs consist of numerous internal ramified aquatic canals, which terminate in the anus, they commence on the surface by minute absorbing fleshy tubes. Sometimes the mouth is furnished with osseous pieces, and teeth like those of an Echinus. In the Holothuria and some other genera of this order, the body is furnished with numerous cylindrical retractile papilla:, disposed in longitu dinal rows along the outer surface, and serving as feet for progressive motion. These organs, how ever, are variously disposed in the different genera. They arc marine animals, and are found free and solitary at the bottom of the sea. Their nervous system presents several ganglia connected by nervous filaments, and disposed around the en trance to the intestinal canal. The genera belong ing to this order are, 1. Bonellus. 5. Molpadia. 8. Fistularia.
2 Sipunculus. 6. Holothuria. 9. Phantapus.
3. Minyas. 7. Actinopus. 10. Phalloides.
4. Priapulus.
The Radiata of this order have the body of a globular ovoidal or depressed form, covered with a calcareous shell, to the surface of which are articula ted numerous movable conical spines. The organs of motion in form of fleshy cylindrical tubes or suckers extend from minute perforations disposed in a radiated manner along the shell. The mouth is generally furnished with a complicated osseous frame-work containing five teeth lodged in alveoli. The intestine extends from the mouth in a con voluted form attached to the sides of the body by a distinct mesentery, and the anus is always dis tinct from the mouth. Vessels for a partial circu lation are seen extending along the course of the intestine and on the mesentery. These animals are marine, and they exist free and single. They pre sent no distinct organs of sex, but possess all equally ovaria, which open, each by a separate orifice, generally around the anus. The ovaria are the parts which are eaten in the common sea urshin, or Echinus esculentus. The genera of this order are, 1. Echinus. 6. Cassidula. 10. Ananchites.
2. Cidaris. 7. Fibularia. 11. Spatangus.
3. Echinoneus. 8. Clypeaster. 12. Brisoides.
4. Galerita. 9. Scutella. 13. Brissus, 5. The animals of this order arc by the star-like form of their body, which is divided into a variable number of rays. The mouth is
situate in the centre of these rays, and on the lower surface as in most other Radiata. There is no anus distinct from the mouth, but numerous rami fied cceea extend from the sides of the stomach into all the arms, to the sides of which they are connected by a mesentery. The respiratory organs are minute cylindrical retractile tubes, disposed on the upper surface of the body as in the preceding orders, and which convey water into the interior of the body. Vessels are seen forming a plexus round the stomach, coming from the mesentery and pass ing towards the aquatic tracheae, apparently for a circulation. And in the asterias ganglia are ob served disposed around the stomach, connected by filaments, and sending nerves to the stomach, to the arms, to the organs of respiration, and to the skin. The ovaria, like a double cluster of grapes in each arm, terminate in two ducts at the place of junc tion of each of the arms. They have no organs of sex or for impregnation. The Asteroida are all marine animals, and from their vast abundance they are employed as a manure on the coasts of this country and of France. Their forms are re markably regular and symmetrical, and their colours in the living state are lively and often beautifully variegated. The genera of this order are, 1. Asterias. 3. Comatula. 5. Pentacrinus.
2. Ophiura. 4. Euryale. 6. Encrinus.
The animals of this order, like the Holothurida, have generally a lengthened cylindrical body, co vered with a coreaceous contractile and highly ir ritable integument. Like the Asteroida they have no anus distinct from the mouth. The disposition of their tubular tentacula in several rows around the mouth, their circular form, and the beautiful colours which decorate their surface, give them the appearance of flowers, from which the name of the order is derived. They are marine animals, and remain attached spontaneously by their base to submarine bodies. They feed on testaceous and other animals, which they seize with their ten tacula when brought within their reach by the tide or other acident, and the tentacula and whole upper surface of their body is for this purpose covered with a very adhesive, thick, glutinous secretion. In the Actinix nerves are seen around the base of the stomach, and the ovaria lie between the stomach and the perpendicular folds of the parietes of the body. The young are produced already formed, and pass out through the stomach. They compose the order of fixed Aealepbx of Cuvier. The genera of this order are, 1. Actinia. 2. Zoanthus. 3. Lucernaria.