Page:The New International Encyclopædia 1st ed. v. 14.djvu/442

NERVOUS SYSTEM. 392 XTESSELBODE. Tlic paired, coiiipouml eyes are covered liy a transparent eutieula. A single visual element of the compound eye is called an onimatidium. Kacli clement is composed of two parts, an outer vitreous and an inner sensory group of cells. The latter is known as the rhalKlonie and is made up of the retinule and a refracting rod. Kach onimatidium is in a state of optical isolati(jn. Fibres pass from the optic j;aii<;lia to the retinule. The organs of touch are hristled cells on the appendages, especially on the antennic, the palpi, and on other parts of the body. The olfact(uy organs of the crayfish consist of a number of delicate seta- borne on the antennules. The audi- tory organ is a pit ujKjn the exterior and lined with auditory setic. Grains of sand in the case of Crustacea often serve the function of otoliths. These must be renewed after each molt. .Amphioxus possesses an olfactory pit. It is a ciliated depre-sion at the level of the anterior end of the brain. It is connected with the olfac- tory lobe of the brain. This pit may correspond with the 'pituitary body' of Urochorda and C'raniata. The organ of sight is merely a pig- ment spot. It is median and without a lens. Cells supposed to have a sensory function occur on the roof of the oral hood and tactile cells occur on the buccal cirri. The organs of special sense of vertebrates com- prise various kinds of tactile organs, of which may he mentioned the lateral-line organs, which in structure resemble the organs of eh*topods. The lateral-line organs occur in amphibians and fishes, and are supposed to perceive vibrations in the water and also to have an auditcuy func- tion. End-bulb organs likewise occur here and there over the entire surface of fishes. From amphibians upward they are restricted to the mouth. Specialized tactile cells, such as the Pacinian corpuscles of the duck's beak, occur in difl'crent vertebrates. The olfactory organ is in fishes a pair of sensory pits near the anterior end of the snout. From the Dipnoi onward these pits communicate with the mouth cavity as well as with the ex- terior. From the Dipnoi onwanl also these organs are more or less inclosed either in a cartilaginous capsule or they are included in the cranium. The internal nostrils with their glamls are developed in Dijinoi and .mphibia. The nasal cavity of Lacertilia is divided into an outer and an inner jiart. From the crocodiles onwanl the nasal organs recede in correspondence with the forward extension of the facial region. Hoth in repliles an<l birds there is only one true turbinal Ikjuc in the nasal canal. Heeause of the extreme facial devel(i]iment of the skull of mam- mals, tile nasal cavity is prttportionatcly larger. The turbinals co!i-.|.i|Ucntly greatly develop here. The nasal cavity "I mamnutls connnimicates with certain sinuses of the face. The .sensitive elements of the vertebrate eye develop from outgrowths, primary optic vesicles, of the brain. The pigment epitlu-lium develops from an inpocketing of this vesicle. The lens develops from thickened epidernnil cells. In cydostomes the lens and iris arc absent and the sclerotic and cornea arc undifrcrentiated. A plolinlar lens is |)rescnt in the eyes of true fishes. .Amiihibian eves are simpler than those of fishes, but a ciliary muscle is present. The sclerotic is cartilaginous with bony plates oven in lizards and birds. The eye-ball of nocturnal birds is elongated and tubular. The iris of birds may be highly colored owing to the presence both of pigment and of fat globules. The ee of mam- mals is more or less inclosed in the bony orbit, the sclerotic is fibrous, and the fibres of the optic nerve pass into the retinal cells. The retina is histologically a complicated structure and consists of seven layers; the light must pass through all the layers in order to reach the innermost rod and cone layer. The region of acutest vision is the fovea centralis, where only the cones persist. As to aiulitory organs, it is the sacculus and cochlea in the vertebrate ear that attain a higher and higher degree of develo|)ment. In fishes the cochlea is a knob-like appendage of the sacculus. In amiihibiaus it is constricted off from the sac- culus and only remains connected by a strand of cells. In mammals the cochlea becomes spirally coiled. There are three coils in man. A chain of three auditory ossicles ajipear in the higher vertebrates. LiTEH.TUEE: Wiedersheim, Comparative Anat- omy of Vertebrates (Eng. trans., London, 1897) ; Kingsley, Text-bvolc of Vcrtctirate Zoiiluriy (New York, 1S99) ; Lang, Text-book of Comjiuratirc Aiiiitom!/ (London. lSI)I-!)(i| : Lang, "L'cbcr pri- miire Jlctamerie des Xeuralrohres ilcr. Vertebra- ten," in Sit.tiiiifisherirhte (hr kuitUttUh huicrisch- <ii Akdilrmie der Wissenschaftcn (.Mimich, 1885). NES'BIT, Edith. An English poet. See Bi...i). EuiTH Xesbit. NESS, Loch. A lake in the County of Inver- ness, Scotland. It occupies, together with Loch l.ocliy and Loch Linnhc, the bottom of the great fracture which in an almost straight line severs the northwestern Highlands from the rest of Scotland, and which is known as Glen More, or Great Glen (.Map: Scotland. D 2). Loch Xesa is 2.3 miles long, from one-half to one and one- half miles broad, and connected by rivers and canals with the Firth of l.cirnc on the southwest and Jloray Firtb on the northeast. It receives the waters of several small rivers, and is sur- rounded by high and steep mountains which make the scenery very |)icturcsi|ue. Owing to its im- mense depth tile Loeli never freezes. NESSELRODE, nes'sd-ro'dc, ICvrl RonERT, ('(iinit ( 17801S()2). .- Russian diplomat, born at Lisbon, where his father then resided as Rus- sian .Ambassador. The young man devoted him- .self to a diplomatic career, won the confidence of the Emperor. .-Mexander I., and was in the diplomatic suite of the latter during the eventful year of 181.3 and the negotiations at Paris after the first defeat of Xapoleon. lie was one of the signers of the treaty of the i|uailruple alliance at Chaiimont. and also of the treaty with Mar- shal .Marinont for the surrender of Paris. He was one of the most ]irominent of the plenipo- tentiaries in the Congress of Vienna, and in 1816 became Minister of Foreign .All'airs. and accom- panied the Emperor .lexander to the congresses of Aix-la-Clinpelle. Troppau. Laibach, and Ve- rona, where he always advocated a policy of mod- eration. Under Nicholas I., Ncsselrode became Vice-chancellor (1829) and Imperial Chan- cellor (1844). It fell to him to direct the Russian policy in the affairs of Greece and Turkey, Xesselrode was opposed to the policy which brousibt on the war of 18.")3-.')ri and retired from the Foreign Office after signing the Treaty