1? The Shell-Collector’'s Handbook. 
viscero-pleural ganglia nerves pass to the viscera and 
the body-wall (pallial nerves). The supra- and sub- 
esophageal ganglia are spoken of collectively as the 
nerve collar. 
The supra- and sub-cesophageal ganglia communicate 
with each other by a pair of connectives, and between 
these the auditory nerve courses to the auditory 
organ. 
A microscopic examination of a ganglion shows it 
to consist of unipolar, sometimes bipolar, nerve cells, 
imbedded in a matrix of neurilemma, which in the 
Zonites is said to contain unstriped muscle fibres. 
THE Avpirory OrcGans.—The auditory organs 
(otocysts) are a pair of small rounded sacs, situated 
either in the substance of the pedal ganglia or in 
close relation with them ; and in the genus Paludina 
are moveable by muscles. Each contains in its 
interior a large number of calcareous granules 
(otoliths), which strike upon the terminal filaments of 
the auditory nerve, and thus communicate a wave of 
change to the supra-cesophageal ganglia. In some 
Pulmonata the otocyst is in communication by a 
canal with the external world. 
THE Eyes.—The eyes are carried on the distal ends 
of the posterior tentacles, and, from this reason, this 
pair of tentacles has been called the ommatophores. 
They are simple in character, globular or oval in 
contour, and can be regenerated, if destroyed, by the 
animal. Accommodation for long distances seems to 
be defective, for snails cannot distinguish objects till 
they are within a quarter of an inch from the eyes. 
Each eye consists of a cornea, lens, and strongly 
