Outlines of human physiology . s matter is met with wrought either intorounded masses or into flattened chords, to whichgreater or less firmness is given by sheaths of a deli-cate membrane, that is distributed in fine layers andprocesses upon its surface and throughout its sub-stance. A nervous system appears essentially composed oftwo parts ; of a central organ consisting of two chords,one corresponding with either half of the body, uponwhich nodular masses are generally placed; and se-condly, of other chords called nerves, derived from thecentral organ to the sentient surfaces or contractile
Outlines of human physiology . s matter is met with wrought either intorounded masses or into flattened chords, to whichgreater or less firmness is given by sheaths of a deli-cate membrane, that is distributed in fine layers andprocesses upon its surface and throughout its sub-stance. A nervous system appears essentially composed oftwo parts ; of a central organ consisting of two chords,one corresponding with either half of the body, uponwhich nodular masses are generally placed; and se-condly, of other chords called nerves, derived from thecentral organ to the sentient surfaces or contractileparts of the animal. Nervous Si/stem of Radiated Animals. 253 1. In the star-fish (a radiated animal) the centralorgan consists of a ring of white nervous matter, whichsurrounds the orifice of the stomach, and gives offopposite to the centre of each ray nerves for itssupply. The adjoined figure, meant to represent the nervoussystem of a star fish, is very imperfectly copied fromone of Tiedemanns beautiful and elaborate 254 Ne7vous Sijstem of Articulated Anhnah. 2, In the centipede (anarticulated animal) the cen-tral organ consists of a dou-ble chord extending itswhole length immediatelywithin the integuments ofthe abdomen: at the mid-dle of each segment a no-dule is formed upon eachchord, from which the nervesof that part are foremost of this seriesof pairs of nodules is placedbelow the cesophagus, andis joined by two filamentsto another placed above it;from the latter are given offnerves to the eyes and tothe antennae. This figure,and the following of a freshwater muscle, are takenfrom preparations in themuseum in Great WindmillStreet. In the fresh-water mus-cle (a species of mollusca)the central organ consistsof, a nodule on each sideof the cesophagus, a dou-ble nodule in the foot,and another before the fV h jCj Nervous Si/stem of Mollusca. 265 greater muscle of the shell, which are united togetherby white chords, and distribute nerves to the partsadjoini
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