CHAPTER XI.

ANNULOIDA.

ANNULOIDA (annulus, a ring; and eîdos, form), also termed by Professor Owen, Nematoneura (vîμa, a thread; and veûpov, a nerve).—The members of this and the succeeding sub-kingdoms live either in water or in the interior of other animals; none of them erjoy a free terrestrial existence. The Annuloida are known by the following characters :— They all possess a distinct set of vessels, which have received the name of the "water vascular" or "aquiferous" system. The alimentary canal, when present, is distinct, and usually has both an oral and an anal aperture. A nervous system is present, the ganglia being arranged symmetrically. They often exhibit in their reproduction what is termed "alternation of generation" (vide Appendix). They are divided into

1. Echinodermata.
2. Scolecida.

1. ECHINODERMATA (exivos, a hedgehog; and dépμa, a skin). The members of this group always have their integument more or less hardened by calcareous matter. An alimentary canal is always present. The water-vascular system is termed the "ambulacral" (ambulo, I walk) system, because it is often used in locomotion. The nervous system forms a ring round the gullet, from which branches proceed to the different parts of the body. They are divided into the following orders :-

I. HOLOTHURIDEA (¿λo@oúpιov; and eîdos, form).—Body elongated and worm-like; integument thick and contractile, often destitute of calcareous matter; mouth surrounded by tentacles; a distinct anus always present; ambulacral system sometimes rudimentary. The members of this order are commonly called sea "cucumbers 66 or trepangs."

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II. ECHINOIDEA (èxîvos, a hedgehog; and eîdos. form).— Body covered with a test or shell, composed (in all existing forms) of ten calcareous zones. The five larger zones are imperforate, and termed "inter-ambulacral areas;" the five smaller ones are perforated with holes for the ambulacral tube feet, and termed "ambulacral areas.' The test is covered with tubercles carrying spines. The mouth is guarded by five teeth, popularly called "Aristotle's lantern." The members of this order are commonly called " sea hedgehogs, sea urchins," or sea eggs."

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III. ASTEROIDEA (ǎσтρov, a star; and eîdos).—Body starshaped, consisting of a central portion, surrounded with five or more arms, containing prolongations from the stomach; integument thick, and hardened with calcareous matter. Nervous system truly radiate; oral and anal apertures present. The members of this order are popularly known as star-fish."

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IV. CRINOIDEA (кpívov, a lily; and eldos, form).—Body covered by calcareous matter, and fixed during the whole or a portion of the animal's existence by a flexible stalk. There are five or more arms; alimentary canal has both an oral and anal aperture. The members of this order were formerly numerous, but are now scarce; they comprise the "feather stars" 66 or sea lilies."

V. OPHIUROIDEA (opis, a serpent; óùpa, a tail; and eîdos).— Body circular, to which are attached five arms that do not contain prolongations of the stomach; integument hardened

workers (neutral females), about six hundred drones (males), and one queen bee, or perfect female; once in four or five years the queen bee selects a mate from among the drones, and by this single act of coitus the innumerable ova to which she subsequently gives birth are impregnated; the drones are now killed and expelled from the hive as useless. The following account of the construction of the bee-hive is taken from Dallas:-"We never, however, except at the period of swarming, meet with more than one female in the hive. The whole duty of the construction of the comb and the care of the young devolve upon the workers, whose incessant activity has rendered them the most appropriate types of industry. The comb, as is well known, consists of beautiful hexagonal cells, constructed with mathematical accuracy; it is perpendicular, and composed of a double series of cells placed end to end in such a manner that the end of each cell is closed by three waxen plates, each of which also assists in completing one of the cells of the other side of the comb. By this arrangement the greatest possible number of cells may be constructed in a given space with the smallest amount of material. In these cells the eggs are laid; here also the larvæ are brought to maturity by the care of the workers; and when no longer required as nurseries for the young, they are employed as a store for honey. The eggs which are to give birth to males are placed in cells a little larger than those of the workers. Those from which females, or queens, are to be produced are deposited in cells of peculiar construction, and the larvæ are fed upon a different food from that of the workers. When the population of the hive has grown too large, a portion of the workers emigrate, accompanied by a young queen. This is termed "swarming."

Insects have been divided into the following orders:

Ametabolic (à, not; and μεταβόλος, changeable).

Hemi-metabolic (μ. half; and μεταβόλος).

Holo-metabolic (8λos, whole; and μeтaΒόλος).

1. Anoplura (άvorλos, unarmed; and oùpá, tail)—e.g., louse (pediculus).

2. Mallophaga (μaλλós, wool; and payei, to feed)-Bird louse.

3. Thysanura (Oúσavos, a fringe; and oupá, the tail-Spring tail (podura).

4. Hemiptera (ñμ; and πтeρóv, a wing)Plant lice (aphides).

5. Orthoptera (opeóv, erect; and πτEρóν)———Cockroach (blattina).

6. Neuroptera (veûpov, a sinew; and TTEρÓV)-Dragon flies (libellulidæ).

7. Hymenoptera (suhv, a membrane; and TTEрÓV)-Bees and wasps.

8. Aphaniptera (apavñ, unseen; and TTEрά, wings) Flea (pulex).

9. Diptera (dúo, two; and Tтeрà)-House fly (musca).

10. Lepidoptera (Aeπís, a scale; eidos, form; and TTEрà)-Butterflies,

moths.

11. Strepsiptera (σrpépw, I twist; and TTЄρà)-Stylops.

12. Coleoptera (Koλeós, a sheath; and πTЄρà)-Beetles.

The first three orders undergo no metamorphose whatever; the next three undergo a partial metamorphose; while the last six undergo a complete one.

2. ARACHNIDA (¿páxvns, a spider; and eldos).—The members of this class are easily distinguished by the following characters :-The head is always united to the thorax, so as to constitute a cephalo-thorax; the integument is usually hardened with chitine, but sometimes remains soft; there are always four pair of legs, never more; wings are always absent, and the abdomen never has limbs of any kind con

with calcareous matter. There is an oral aperture, but no anal. This order contains the sand stars and brittle stars.

VI. CYSTOIDEA (kúσtis, a bladder; and eldos).) Both these orders are VII. BLASTOIDEA (BλáσTos, a shoot; and eîdos).) extinct.

2. SCOLECIDA (σkwλn), a worm; and eîdos).—The animals comprised in this division never have their integument hardened with calcareous matter. The alimentary canal is frequently absent, and the nervous system is very rudimentary, consisting only of one or two ganglia. They all, however, possess a water-vascular system. Many are internal parasites, and are reproduced by an alternation of generations. They are divided into