. Outlines of zoology. loped,but there is a supra-ossophageal gangli-onic commissure from which the visceraland pedal cords extend backwards alongthe whole length of the body. There areno special sense organs on the head,which is but slightly differentiated ; butthe pallial sense organs are usually numer-ous and varied. A twisted gut runsthrough the body, surrounded by a diffusedigestive gland. There is a radula in themouth. The heart is median and pos-terior, and consists of a ventricle andtwo to eight auricles. There are twosymmetrical nephridia opening posteriorly,and consisting of much - b
. Outlines of zoology. loped,but there is a supra-ossophageal gangli-onic commissure from which the visceraland pedal cords extend backwards alongthe whole length of the body. There areno special sense organs on the head,which is but slightly differentiated ; butthe pallial sense organs are usually numer-ous and varied. A twisted gut runsthrough the body, surrounded by a diffusedigestive gland. There is a radula in themouth. The heart is median and pos-terior, and consists of a ventricle andtwo to eight auricles. There are twosymmetrical nephridia opening posteriorly,and consisting of much - branched sexes are separate; a single repro-ductive organ extends dorsally betweengut and aorta almost the whole lengthof the body; the genital ducts are pairedand open posteriorly in front of theexcretory apertures. The ova, withchitinous spiny shells, are usually re-tained for some time by the female be-tween the mantle and the gills. The, segmentation is holoblastic, and a gastrulais formed by Fig. 227.—Dorsal viewof nervous system ofAcanthochiton. —AfterPelseneer. I, Upper buccal commissure; 2, upper buccal ganglion ; 3, stomatogastric commis-sure; 4, labial commissure;5, sub-radular ganglia; 6,anterior pedal commissure;7, pedal nerve with pallio-pedal connections ; 8,supra-rectal pallial com-missure; 9, pallial nerve;zo, anastomosis of branchesof pedal nerves; iT,stomato-gastric ganglia ; 12, oeso-phageal nerves; 13,cerebral,commissure. GASTEROPODA. 419
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Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
