The brain as an organ of mind . branches to this muscle,to each half of the mantle, and the gills (c, c). Other more active Lamellibranchs possess a muscularappendage known as the foot, which is in relation with anadditional single or double nervous ganglion (pedal), andis used in various ways as an organ of locomotion. Speak-ing of the diverse uses of the foot among bivalves. says :* To some which rise to the surface of thewater it acts, by its expansion, as a float; to others itserves by its bent form as an instrument to drag Fig. 22. —Nervous System of anOyster. (Todd af
The brain as an organ of mind . branches to this muscle,to each half of the mantle, and the gills (c, c). Other more active Lamellibranchs possess a muscularappendage known as the foot, which is in relation with anadditional single or double nervous ganglion (pedal), andis used in various ways as an organ of locomotion. Speak-ing of the diverse uses of the foot among bivalves. says :* To some which rise to the surface of thewater it acts, by its expansion, as a float; to others itserves by its bent form as an instrument to drag Fig. 22. —Nervous System of anOyster. (Todd aftei Garner.) a, a, (double); /, labial nerves c, c,branchial nerves; d, d, commis-sures Ijetween labial and them along the sands : to a third family it is Lect. on Comp. Anat. of Invert. Animals, p. 505. 74 THE NERVOUS SYSTEM OF MOLLUSKS. harrowing organ ; to many it aids in the execution ofshort leaps. The hivalves possessing a foot, therefore, present threepairs of ganglia instead of two—the anterior or lahial,. Fig. 23 —Nervous Systoin of th; Conmiou Mussel. (After Owen.) I, Tvabial gangliaconnected by a short conini ssu o above or in front of the mouth; b, !>, branchialganglia similarly connected, and also united by very long cords (</, d) witli the labialganglia; 2K bilobed pedal ganglion sending branches to tlie muscular foot (,r), connected with the auditory saccules (s); h, h, circum-pallial plexus;y, byssus. by which the animal attaches itself to external substances. the posterior or hranchial, and the inferior or * occasionally liai)peiis that the ganglia of the posterioror even of the inferior pair may hecome approximated andfused into one. Chap. IV.] THE NERVOUS SYSTEM OF MOLLUSKS. 75 The fusion of the posterior ganglia takes place, as in theOyster (fig. 22, b), when the branchise from which theyreceive nerves {c, c) come close together posteriorly. Onthe other hand, in those Mollusks in which the branchiaBare farther apar
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