INTERNAL ANATOMY. 3393 
of the fifth nerve, but runs along its outer border, inclosed in the same sheath for 
atime. The nerve terminates in the large deep blue eye, which is deeply buried 
below the surface in the integument, behind the rhinophores. Whether the optic 
nerve arises from a separate ganglion distinguishable from the cerebral can only 
be determined by serial sections, which have not been made of this region. 
The sixth, or acoustic nerve is extremely delicate and can be traced only 
with difficulty. It can be made out as originating from the side of the cerebral 
ganglion close in front of the origin of the cerebro-pedal connective, which it 
accompanies to the dorsal surface of the pedal ganglion, terminating in the 
minute otic ganglion and otocyst, both deeply imbedded in the thick connective- 
tissue capsule which covers the pedal group. It is shown on the right side only 
in Plate 2, fig. 1, at c6, where it reaches the pedal ganglion, but was removed 
with the connective-tissue capsule on the opposite side. The long cerebro- 
buccal connectives, c-b con, arise from the antero-lateral face of the cerebral 
ganglia and pass obliquely downward and backward to the buccal ganglia 
(Plate 3, fig. 3), situated upon the ventro-posterior face of the pharyngeal bulb, 
immediately below the beginning of the oesophagus. 
The cerebro-pedal connectives, c-p con, arise from the midlateral face of 
the cerebral ganglia and are united in a common broad sheath for the most 
of their extent with the cerebro-pleural connectives, c-pl con, which arise behind 
them from the postero-lateral face of the same ganglia. Together they encircle 
the pharyngeal bulb in a long course, and unite below with the pedal and the 
pleural ganglia respectively, as shown in the lower half of the figure. They 
measure 19.0 mm. in length, being approximately equal in this respect. A short 
distance from the ventral group of ganglia they separate into two distinct 
trunks. 
Pedal ganglia.— The ventral portion of the circumoesophageal ring is 
completed by the pedal and the pleural ganglia, represented in dorsal view 
in the lower half of Plate 2, fig. 1, and in ventral view in Plate 5, fig. 2. The 
whole complex is united into a single lenticular mass by a thick connective- 
tissue capsule, which must be carefully dissected away before the relations of 
the ganglia and nerves may be recognized. In both the figures cited they are 
represented as entirely free from this sheath. The pedal ganglia are of a flat- 
tened elliptical shape, united by a short and broad commissure, 1.3 mm. long 
by 1.0 mm. broad, and by a slender parapedal commissure, passing below the 
aorta (Plate 5, fig. 2, p-p.c). The two ganglia are of nearly equal size, approxi- 
mating 2.3 mm. wide by 3.0 mm. long. 
