INTERNAL ANATOMY. 333 



of the fifth nerve, but runs along its outer border, inclosed in the same sheath for 

 a time. The nerve terminates in the large deep blue eye, which is deeply buried 

 below the surface in the integument, behind the rhinophorcs. Whether the optic 

 nerve arises from a separate ganghon 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 deUcate 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 

 miimte 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 cereijro- 

 buccal connectives, c-b con, arise from the antero-lateral face of the cerebral 

 gangUa 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 gangUa, 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 comaective- 

 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 nun. 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. 



