The Cambridge natural history . ns Drap.)eg, eg, cerebral ganglia ; e, e, eyes ; os,osphradium ; at, ot, otocysts ; 2^-(h P-U)pedal ganglia ; j), , pleural ganglia;, supraiutestiual ganglion ; , sub-intestinal ganglion ; , tentacle nerve ;, visceral ganglion. (After Lacaze-Duthiers.) commissm-es; the visceral loop is rather long, and the two vis-ceral ganglia are adjacent to the anus. Pelecypoda.—The nervous system in the Pelecypoda is thesimplest type in which well-marked ganglionic centres occur. Theganglia are few, symmetrically placed, and are usually at a con-siderabl
The Cambridge natural history . ns Drap.)eg, eg, cerebral ganglia ; e, e, eyes ; os,osphradium ; at, ot, otocysts ; 2^-(h P-U)pedal ganglia ; j), , pleural ganglia;, supraiutestiual ganglion ; , sub-intestinal ganglion ; , tentacle nerve ;, visceral ganglion. (After Lacaze-Duthiers.) commissm-es; the visceral loop is rather long, and the two vis-ceral ganglia are adjacent to the anus. Pelecypoda.—The nervous system in the Pelecypoda is thesimplest type in which well-marked ganglionic centres occur. Theganglia are few, symmetrically placed, and are usually at a con-siderable distance apart. There are, as a rule, three distinct pairsof ganglia, the cerebral (cerebro-pleural), pedal, and visceral. Thecerebral are formed by the fusion of the cerebral and pleuralganglia, which however, in some cases (Protobranchiata) continuedistinct.^ They lie above or on each side of the mouth, united^ This fusion of the cerobral ami pleural ganglia and the consequent union of the 2o6 NERVOUS SYSTEM IN PELECYPODA. by a commissure of varying length. Another pair of com-missures unites them with the pedal ganglia, which are placedat the base of the foot, and are usually ^-ery close together,sometimes (as in Anodonta) becoming partially fused. The length of these commissures de-pends upon the distance betweenmouth and foot; tlius they arcvery long in Myii and Modiuhi,and very short in Fecten. Incases where the foot is rudimen-tary or Ijecomes aborted througlidisuse ( Ostrea), tlie pedalganglia may dwindle or disappearaltogether. The visceral gangliaare on the ventral side of theposterior adductor muscle, beneaththe rectum, and innervate thel)raiic]iiae, osphradia, and tliewhole of the visceral sac. A pairof cereltro - visceral commissurestraverses the base of the foot,surrounding it witli a compara-tively short loop (compare , ), while a long connuis-sme, which runs round the entire edge of tlie mantle, and sup-plies branching nerves to the mantle bor
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
