. The evolution and function of living purposive matter . known as the Echinoderms, whichinclude the starfish with its body and five radiatingarms and their numerous ambulacral feet or musculartubes which end ina plate or means of thesesuckers the feetcling to any solidsubstance thatcomes within reachof the animalsarms. The nervousstructure of con-sists mainly of acentral systemwhich always re- tnina afr-riTicr inrlipn. f- ??—Diagram of the neivous [syslcm of arams SMOrig llimua- g^j^],,,],. a, central nerve-Hue siinounding tlie tions of its epithelial »!; ? p*™!
. The evolution and function of living purposive matter . known as the Echinoderms, whichinclude the starfish with its body and five radiatingarms and their numerous ambulacral feet or musculartubes which end ina plate or means of thesesuckers the feetcling to any solidsubstance thatcomes within reachof the animalsarms. The nervousstructure of con-sists mainly of acentral systemwhich always re- tnina afr-riTicr inrlipn. f- ??—Diagram of the neivous [syslcm of arams SMOrig llimua- g^j^],,,],. a, central nerve-Hue siinounding tlie tions of its epithelial »!; ? p*™! <^^» °««™^- (J- i-oeb,origin. It forms a ring surrounding the animals mouth from whichnerves radiate to each of the arms and gives offbranches to the various muscular structures, includingthose of the ambulacral feet (Fig. 7). In the snake-armed starfish (Ophiocoma echinata)a second or deep system of motor nerves exists, thesuperficial system at the same time being sensory infunction. The sensory organs of this class of animals are but. 38 THE EVOLUTION OF PUBPOSIVE MATTER ill developed, and like the nervous system are derivedfrom differentiated forms of the outer sensitive layerof living matter. Pigment cells exist in elevations ofthe ends of the tentacles and are known as eye specks,they lie on separate points of the optic pad and areconnected to subjacent ganglionic cells by means ofnerve fibres, and in this way also with the generalnervous^system of the animal. The flat worms (Platy-helmia) are mostly para-sitic, their nervous systemas a rule consists of anumber of single ganghonicnerve cells in front of thepharynx or opening whichleads to the animals diges-tive organs (Fig. 8). The nervous system,although less immediatelya part of the outer (ecto-derm) layer of cells than isthe case with polyps andjelly-fish, is neverthelessclearly derived from theliving matter of this , as most of the flat worms do, a parasiticexistence, they do not require the
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Keywords: ., bookcentury1900, bookdec, booksubjectbrain, booksubjectphysiology
