5

.E75.

1866

Sect. 2

V. 4 Виви

LONDON:

BRADBURY, EVANS, AND CO., PRINTERS, WHITEFRIARS.

THE UNIVERSITY OF MICHIGAN

DEARBORN CAMPUS LIBRARY

де

5 1E49

Division II

V. 4 - 1,63

are always inhabitants of fresh water: a single instance of one of these Neritina having wandered into the sea, they may, they say, perhaps have had to cite. The Nerits have a particular and distinctive appearance: they pass a part of their life out of the water without ever removing to a distance from it. Those which haunt streams or marshes may adhere to the leaves of trees, but without going on land. Those which are found on land are carried there by Paguri or by some accident. Marine Nerits are also seen at the mouth of rivers; and Messrs. Quoy and Gaimard remark that these are transitions which nearly all the molluscs undergo without suffering much.

The genus Nerita is described separately. [NERITA.]

Neritina has the shell rather thick at the aperture, but extensively absorbed inside; outer lip acute, inner straight, denticulated; operculum shelly, with a flexible border, slightly toothed on its straight edge.

N. pulligera has the shell ovate, slightly striated, blackish-brown; the outer lip dilated, thin, white within, the margin acute, the inner border yellowish; the inner lip toothed. (Lam.)

This fine species is uniform chestnut, with the striae of growth strongly marked; these converge on the spire, which is covered by the right lip.

The animal has long delicate tentacles, which are yellowish soiled with brown. The head and sides of the foot are yellow, spotted with brown and black. The under part of the foot is reddish.

The operculum is large, of an apple-green colour, with black transverse bands proceeding to converge towards the spire: its contour has a reddish line. ('Astrolabe.')

The drawing from which Messrs. Quoy and Gaimard have figured this species was made at Umata in the island of Guam. They state that there are also Nerita pulligere at Vanikoro. They found on the trees dead shells whose spire was always corroded, and they inquire whether they had been brought there, or whether the animal had died after having ascended the trees. They state as a remarkable fact, that in a great number of individuals of this species they found in the liver a small knot of worms, some of which were not less than 17 lines in length. They were pointed at both ends, like Lumbrici, or Round Worins.

Pileolus has the shell limpet-like above, with a subcentral apex; concave beneath, with a small semilunar aperture, and a columellar disc, surrounded by a broad continuous peristome. The species are only known as fossil.

Upwards of 100 recent species of Nerita and 70 species of Neritina have been described. The fossil species of Nerita amount to 60, and of Neriiina to 20. Nerita is found in the Lias, and Neritina in the Eocene Formation.

Navicella.-With the exception of the disposition of its operculum and of the muscles of attachment to the shell, the animal may be said to be nearly similar to that of Nerita. Its head is large, convex, notched, a little auriculated anteriorly, carrying two long and very pointed tentacles, having the eyes at their base, on a rather elongated pedicle. The foot is regularly oval, and does not overborder the shell; at its union with the mantle, near its root, it presents a remarkable bourrelet, which is due to the internal disposition of the operculum. It is pale-yellow below, deeper upon the sides, with spots of deep-brown, as is the case with the head and the ocular peduncles; only the tentacles have a smoked colour, with black and very delicate longitudinal striæ. Mantle light yellow.

The form, and especially the position, of the operculum of Navicella, are so abnormal, that it may be said that it is not a true operculum, and that it is situated in the foot. But it is an evident operculum, and its place is, as in all the Cephalous Molluscs which are provided with that organ, above the foot. Its form is subquadrilateral; it is adherent throughout its lower surface, free on its upper surface, and terminated behind by a cartilaginous part, by means of which it increases. It is carried, as in the Natica, by a very small appendage of the foot, which overborders it a little behind. But that which renders it so abnormal is, that the foot, which is really subtrachelian, that is, only attached below to the body, is united, nearly throughout the rest of its length, to the visceral mass by the continuation of the skin which envelopes it; whence it results that the operculum seems to be contained in a sort of pouch situated between the foot and the viscera, and whose aperture, in the form of a transversal slit, is at the posterior extremity of the body. This disposition of the operculum

a, animal in the shell, seen from below; b, operculum.

The genus Natica, sometimes made the type of a family (Naticida), has been included with the Neritida.

Messrs. Quoy and Gaimard remark, that the Natica are animals to which their foot gives a remarkable aspect. It is a long oval lamella, ordinarily squared in front, oval behind, and doubled; anteriorly, where it is widest, it is a thick escutcheon, a little auriculated, which ascends on the front of the shell, which it covers, at the same time that it hides all the head of the auimal, of which ordinarily nothing but the tentacles appear; a groove on each side indicates the two parts of the foot.

The posterior escutcheon, which is less considerable, supports the operculum, which it overborders in order to cover the left lip and the extremity of the shell. There are individuals in which it has the same size as the foot, from which it is distinguished by a circular groove. Thus, observe these zoologists, throughout their development the Natica resemble a mass of flesh, on the summit of which one perceives a part of the shell. The operculum, although very large, is not apparent; placed transversely, it is hidden by the extremity of the shell, which contains the mass of viscera. A very small muscle binds all this development of flesh to a rather slight columella. The rest of the animal, which is but slightly spiral, offers nothing remark

able.

Dr. J. E. Gray makes the Naticide the first family of his second section, Eriophthalma (Edriopthalma ?), of his second order Phytophaga. Under the Naticida he comprises the following genera:Natica, Neverita, Nacca, Cepatia, Polinices, Mammilla, Cernina, Globulus, Naticina, Cryptostoma, Stylina (?), Radula (?), and Neritopsis. In Woodward's Manual of the Mollusca' the Naticida include the genera Natica, Sigaretus, Lamellaria, Narica, and Velutina.

Ninety recent species of Natica have been recorded. They are inhabitants of the Arctic Seas, Great Britain, the Mediterranean and Caspian Seas, India, Australia, China, Panama, and the West Indies. The fossil species amount to 260.

Sigaretus has 26 recent and 10 fossil species.
Lamellaria has 5 recent and 2 fossil species.
Narica has 6 recent and 4 fossil species.

Velutina has 4 recent and 3 fossil species.

In Forbes and Hanley's 'British Mollusca' the following species of Neritida and Naticida are enumerated as British:-Neritina fluviatilis, Natica monilifera, N. nitida, N. sordida, N. Montagui, N. Helicoides, N. pusilla, and N. Kingii.

NERIUM (from vnpós, humid, the habitat of the species), a genus of Plants belonging to the natural order Apocynaceae. It has a hypocrateriform corolla, the orifice surmounted by lacerated multifid processes; segments of the limb contorted; the filaments are inserted into the middle of the tube; the anthers sagittate, adhering by the middle to the stigma; it has two ovaries, a filiform style dilated at the apex, and an obtuse stigma.

N. odoratum has linear-lanceolate leaves, three in a whorl; the segments of the calyx erect; appendages of the corolla filamentous; the anthers bearded at the point. The flowers red or white, with an agreeable musky scent. The bark of the root and the sweet-smelling leaves are supposed by native Indian doctors to act as powerful repellants applied externally. The root, taken internally, acts as a poison.

N. Oleander, Common Oleander, has lanceolate leaves, three in a whorl being beneath, the segments of the corona trifid. It is a native of the Indies, in humid places, but has now become wild in the south of Europe, by the side of streams and the sea-coast. The flowers are rather large and of a bright-red colour. This species contains a great quantity of gallic acid, and a decoction of the leaves or bark forms an acrid stimulating wash, much employed by the poor people in the south of France to cure cutaneous disorders. The peasants in the neighbourhood of Nice use the powdered bark and wood of the Oleander to poison rats. Several cases are also recorded of death from having eaten meat roasted on a spit of Oleander wood.

All the species of Oleander are very showy when in blossom. They thrive well in a light rich soil; and cuttings strike root freely in a moist situation. All of them require a good deal of heat to flower well in this country.

(Don, Dichlamydeous Plants; Lindley, Flora Medica; Burnett, Outlines of Botany.)

NERVOUS SYSTEM. This system constitutes one of the most essential and characteristic parts of the animal frame. It consists of two portions, the Cerebro-Spinal and the Sympathetic, or Ganglionic, each of which, although possessing many things in common, is distinguished by many peculiarities of structure and function.

The Cerebro-Spinal system includes the brain, spinal chord, and the nerves proceeding from these organs. It is through the medium of this part of the nervous system that the functions of mind, sensation, and volition are performed. This part was called by Bichat the Nervous System of Animal Life. The Sympathetic, or Ganglionic, portion was named by Bichat the Nervous System of Organic Life. These names however involve theories which are not confirmed by recent researches. The sympathetic system consists essentially of a chain of ganglia connected by nervous chords, which extends from the cranium to the pelvis along each side of the vertebral column, and from which nerves pass to the abdominal, thoracic, and pelvic viscera. When examined under the microscope the tissue of which the whole nervous system is composed, may be separated into two elements, the Vesicular and the Fibrous. The vesicular nervous matter is gray or cineritious in colour and granular in its texture, containing nucleated nerve-vesicles, and is largely supplied with blood. The fibrous nervous matter is, on the other hand, usually white, and composed of tubular fibres, although in some parts it is gray, and consists of solid fibres; it is also less vascular than the preceding. The former is more immediately associated with the mind, and is the originating seat of the force manifested in nervous actions; while the latter is simply the propagator of impressions made on it. The union of these two kinds of matter constitutes a Nervous Centre, and the threads of fibrous matter which pass to or from it are called Nerves. The smaller nervous centres are termed Ganglia; the larger ones are the Brain and Spinal Chord.

The Tubular Fibre is a tube composed externally of a fine transparent homogeneous membrane, very much resembling the sarcolemma of muscle. Nucleated cells may however be occasionally seen in it, as in fig. 1, which represents a portion of the sciatic nerve of a frog. This may be termed the tubular membrane of nerve. The contents of this tube consist of a soft, semi-fluid, whitish, pulpy substance, which is readily pressed out of its cut extremity. This is termed by

The researches of Kölliker on the intimate structure of the nervous tissue are the most recent, and we subjoin his general account of the nerve-fibres as given in the translation of his Histology' by Messrs. Busk and Huxley :

"The Nerve-Tubes, or Fibres, also termed primitive tubes, or primitive fibres of the nerves, are soft, fine, cylindrical filaments, having a diameter of 0.0005"-001""; they constitute the principal part of the nerves and of the white substance of the central organs, although they are not wanting in the greater part of the gray substance of the latter and in the ganglia. When examined in the recent state and by transmitted light, they appear as clear as water, transparent, and with simple dark contours; by reflected light-glistening, opaline, like fat, in larger quantities together, white, and for the most part their appearance does not indicate that they are composed of different constituent parts. But it is readily seen upon the application of various methods, that they consist of three entirely distinct component structures, viz. of a delicate coat, and a viscid fluid, in the centre of which is a soft but elastic fibre.

"The Coat, or Sheath, of the Nerve-Fibres (Limitary Membrane, Valentin) is an excessively delicate, flexible but elastic, perfectly structureless, and transparent membrane, which, in quite unaltered nerve-fibres, except in certain situations, is altogether invisible. But on the application of suitable reagents, at least in the thicker fibres of the nerves and of the central organs, it comes readily into view, corresponding, in its chemical characters, in all essential particulars,. with the sarcolemma of the muscular fibres. In the finest fibres of the peripheral as well as of the central nervous system, the existence of this membrane has not yet been demonstrated, and it must consequently, for the present, be left undecided whether these fibres possess sheaths or not.

"Within the structureless sheath lies the Nerve-Medulla, or Pulp (Medullary Sheath of Rosenthal and Purkinje; White Substance of