. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). TYPE MOLLUSC A. 281. ance with the absence of metamerism, lacks the ladder-like arrangement which characterizes the Annelida. Nevertheless there are two ganglionic masses, each in typical cases com- posed of two ganglia which may be homologized with the su- pra^scphageal and the most anterior suboesophageal ganglia of the metameric forms, and are known respectively as the <. (Fig. 124, ce) and pedal (pe) ganglia. The foimer lies above the oesophagus behind the bu
. A textbook of invertebrate morphology [microform]. Invertebrates; Morphology (Animals); Invertébrés; Morphologie (Animaux). TYPE MOLLUSC A. 281. ance with the absence of metamerism, lacks the ladder-like arrangement which characterizes the Annelida. Nevertheless there are two ganglionic masses, each in typical cases com- posed of two ganglia which may be homologized with the su- pra^scphageal and the most anterior suboesophageal ganglia of the metameric forms, and are known respectively as the <. (Fig. 124, ce) and pedal (pe) ganglia. The foimer lies above the oesophagus behind the buccal mass and is connected by nerve-cords termed connectives, surrounding the oeso- phagus, with the pedal ganglion. The cerebral ganglion gives off nerves which pass to the eyes and otocysts {ot) and to the tentacular structures of the head, while the pedal ganglion receives its name from the fact that it sends nerves to the muscular mass forming the foot. In addition to this system of nerves and ganglia there is another system highly developed in the Mollusca which would seem to correspond to the visceral system found in some other forms. It consists bu = buccal gauglia. typically of a pair of pleural ganglia (pi), ^^ = cerebral guuglion. one of which lies upon either side of the "' " *'^''^^''*- pharynx, being united by connectives with both the cerebral and pedal gauglia. From each pleural ganglion a nerve-cord passes backwards to unite with one or more visceral ganglia {vi), situated below the intestine near its posterior termination, and on each of these visceral cords a ganglion occurs, the/janeto? ganglion {pa\ from which nerves imss to the gills, or rather to the sense-organ which is in con- nection with them. The pleural ganglia innervate especially the mantle and the body-wall behind the head, the visceral ganglia send branches principally to the various viscera, while the parietal gauglia, iu addition to the branches which go to the gills and their sense
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