(C) Acanthopteri (ǎкavba, a spine; and πτEρóν, a fin, have one or more of the first rays in fins spiny, swim bladder has no duct, scales usually ctenoid.. (D.) Plectognathi (πλéкw, I weave; and yválos, the jaw), maxillary and præmaxillary bones immovably united, ganoid scales and plates. Cyclolabride-Wrasses. Sclerogenidæ Gurnards. Lophiida-Anglers. Balistidæ File-fishes. Ostracionidæ (Õσтρакоν, a shell (E.) Lophobranchii (λópos, ( Hippocampidæ Sea-horses. a tuft; and Bpάyxov), have tufted gills and ganoid scales. ( Syngnathidæ—Pipe-fishes. ; V. MARSIPOBRANCHII (Cyclostomata).—The members of this order possess an elongated, cylindrical body. The symmetrical fins are always absent; the chorda-dorsalis remains persistent; the skull is cartilaginous, and there is no lower jaw. The heart consists of an auricle and ventricle only, there being no bulbus arteriosus. The gills are in the form of small pouches, opening externally by a series of apertures, and communicating internally with the pharynx. They are divided into a. Hag-fishes (myxinidæ), have a sucker-like mouth, furnished with tentacles, and a single serrated fang attached to the palate, by means of which they penetrate the bodies of other fishes, amongst which they are found. The nasal sacs communicate with the pharynx. b. Lampreys (petromyzonidæ) (πéтρos, a stone; μvžáw, I suck; and eldos), have a sucker-like mouth, but no tentacles. The gills open externally by seven apertures, and lead internally into a common tube, which, in turn, opens into the pharynx; in consequence of this arrangement respiration goes on, though the lamprey may be fastened by its mouth to a stone. VI. PHARYNGOBRANCHII.-This order only contains a single fish called the amphioxus lanceolatus, which is the lowest member of the vertebral sub-kingdom. In this animal the skull, lower jaw, symmetrical fins, and heart, are entirely wanting. The chorda-dorsalis is persistent; the mouth is in the form of a longitudinal slit, surrounded with cirri, and leads into a ciliated pharynx, which performs the functions of a respiratory organ. The water that enters the mouth passes through this branchial chamber, and then goes through a number of slits on either side into the cavity of the body, and finally escapes by the abdominal pore, which is situated in front of the anus. End of the Vertebrata. INVERTEBRATA. CHAPTER IX. INVERTEBRATA.-SUB-KINGDOM-MOLLUSCA. We shall now briefly describe the succeeding sub-kingdoms included by Lamark in one great division, which he designated Invertebrata; and although they differ widely from each other in various particulars, they are all distinguished from the Vertebrata by the following characters:—(1.) The entire absence of a vertebral column, lacteal and lymphatic systems, as well as portal venous system. (2.) There is no endoskeleton; when a skeleton is present it is always external, and is called the exo-skeleton; in the cephalopoda, however, the most highly organized of the mollusca, there is an attempt at a rudimentary endo-skeleton in the form of the "cuttle bone' or "pen." (3.) There is only one nervous system, which is supposed to be similar to the sympathetic system of the Vertebrata. (4.) The limbs, when present, are always, directed towards the neural side of the body. (5.) The different organs, so easily demonstrated in the Vertebrata, become variously modified, and gradually disappear, until we arrive at the lowest of the Protozoa, where we find a living animal composed of a single cell, without any organ whatever, and not even possessing an oral or anal aperture. The following are the subkingdoms now most generally recognised: Mollusca (mollis, soft). Molluscoida (mollusca ; and eldos, form). Annulosa (annulus, a ring). Cælenterata (koíλa, hollow; and evTepa, intestines). It will be seen that we do not arrive at the protozoa by a direct line, but by two distinct routes. In the ensuing pages it will be more convenient to describe the molluscoida as a division of the mollusca, not as a distinct sub-kingdom. 66 MOLLUSCA are soft-bodied animals, having a soft and moist skin, termed the mantle, which usually secretes a calcareous covering or shell, hence they are popularly called "shell-fish" (in the naked mollusca the shell is absent). The shell is composed of carbonate of lime, and all recent shells are covered with a layer of animal matter, termed the epidermis" or "periostracum." The shells of molluscs are either univalve, bivalve, or multivalve; they are nonvascular, and grow by the addition of layers to their circumference; if too small, they may be cast off and reproduced; when broken, the fractured extremities cannot unite by any material produced by the shell itself, but are cemented together by newly-formed shell substance secreted by the mantle. As regards their conformation, three principal varieties of shell are enumerated, viz., the “nacreous (nacre, pearl) or "pearly shell," the "porcellaneous" (porcelaine, china), and the "fibrous." The digestive apparatus consists of a mouth, gullet, stomach, intestine, and anus; in a few of the lower forms the intestine ends in a cæcal extremity. The respiratory function is performed by branchiæ in the aquatic forms-by air sacs in the terrestrial. The heart, in the higher mollusca, is systemic, and consists of an auricle and ventricle; the blood is colourless, or has a greenish tinge, and is contained in vessels. 66 99.66 The nervous system, in the mollusca proper, consists of three principal ganglia, called the “cerebral,” pedal," and • parieto-splanchnic," connected together by commissures, hence they have been called "hetero-gangliata” (étepóv, odd; and yǎyyλıov) (Owen); the names given to these ganglia indicate their position and the parts they supply; the gullet is, moreover, surrounded by a nervous collar. In the lower mollusca there is only a single ganglion, giving off filaments in various directions. Organs of smell, sight, and hearing, are believed to exist in all the mollusca proper. Reproduction is almost always sexual, the sexes being usually distinct, but sometimes united in the same individual. The colonies, however, of the polyzoa and tunicata are produced by a process of continuous gemmation. The mollusca are sub-divided into the mollusca proper and the molluscoida. Some naturalists have, however, raised the molluscoida to the rank of a distinct sub-kingdom. The mollusca proper are sub-divided as follows: 1. Odontophora (odoús, a tooth; and popós, bearing), encephala (eyképaλos, brain), or cephalophora (κεφαλή, a head; and popós). 2. Acephala (à, not; and Kepaλ), or headless. Cephalopoda (Kepαλń, and πоús, Gasteropoda (yaσrp, the sto- Lamelli-branchiata (lamella, I. CEPHALOPODA. All the members of this order are marine, carnivorous, and possess great power of locomotion. They have eight or more arms surrounding the mouth. The body is enveloped in a muscular mantle sac, or gill sac, within which are two or more gills; the anterior orifice of this sac is termed the "funnel," or infundibulum, through which the effete water of respiration is expelled, as well as the residue of the food, for the anus opens at the base of the funnel. The body is symmetrical, and divided into an anterior or cephalic portion, and a posterior or trunk containing the viscera. The head is provided with a pair of large eyes, while the mouth is surrounded by eight or more arms, which are usually furnished with rows of suckers or "acetabula; " |