592 
BULLETIN OF THE BUREAU OF FISHERIES 
NERVOUS SYSTEM AND SENSE ORGANS 
The nervous system (fig. 13) comprises a central nervous system of three pairs of 
principal ganglia with commissures and connectives and, in the ganglionic circum- 
pallial nerve, what might be termed a peripheral nervous system. (See Boutan, 
1902, and under "Mantle” in this paper.) 
The three pairs of central ganglia are considerably modified in arrangement. 
The cerebral ganglia are closely united with the pedal ganglia, which are joined one 
to the other without appreciable commissure. (Fig. 14.) The visceral ganglia are 
so fused and developed that they form one large, complex, ganglionic mass (fig. 14) 
and warrant the term visceral ganglion adopted by Dakin (1910). 
The elongate, slightly bilobed, cerebral ganglia are located near the surface 
between lips and foot. At the anterio-dorsal end of each arises the cerebral com- 
missure which passes dorsally in a loop around the oesophagus and connects the 
surface to a small round otocyst, from which arises a threadlike structure termed the 
otocystic canal. For histological detail see Buddenbrock (1915) as to Pecten and 
Field (1922) as to Mytilus. For accounts of the importance of the otocysts as organs 
of balance and control of movement see Buddenbrock (1911 and 1915). They have 
also been considered organs of hearing. The cerebral commissure extends around the 
oesophagus. 
Between the two cerebral ganglia, and connecting them, lie the abutting pedal 
ganglia and the short cerebro-pedal connectives, one of which arises not far from the 
center of the inner side of each cerebral ganglion. From the pedal ganglia arise the 
pedal nerves which enter the foot, subdivide, and become much convoluted. 
The large cerebro-visceral connectives lead diagonally along the stomach and mid- 
gut to the adductor muscle and thence to the visceral ganglion which lies on the 
anterio-ventral surface of this muscle, between it and the visceral mass, but extending 
chiefly to the right so that a large part may be viewed without dissecting away the 
visceral mass. In size, complexity of shape, and number and size of nerves which 
arise from it, the visceral ganglion greatly exceed any of the other central ganglia. 
Figure 13. — Interior view of nervous system. A. P., Anterior paliial 
C AP. C.P.G. 
paired ganglia. From the other end 
extends the large cerebro-visceral 
connective. Near the middle of 
the outer side three nerves arise 
together. The first, or innermost, 
is small and leads to the "tufted” 
lips and may be termed the "labial 
nerve.” The larger, middle one, 
the anterior paliial nerve, sends two 
branches to the circumpallial nerve. 
The outer one supplies the palps 
and is here termed "palpal nerve.” 
In some instances the anterior paliial 
and the palpal nerves continue as 
one for a short distance before sep- 
arating. The fine otocystic nerve 
U ivlh AO. IlilCl 1U1 Vlc-YV Ilv-I V UUo ojulclu. / A ■ J .y ixUlLIiUl paliial 
nerve; B., branchial nerve; C., circumpallial nerve; C. P. G., cerebro- of each of these ganglia arises near 
pedal ganglia; L. P. i-iv, lateral paliial nerves; P P posterior paliial ^ sourC e 0 f the cerebro-pedal COn- 
nerves; V. G., visceral ganglion. The lettered side is the left side _ 1 
nective and leads away from the 
