246 INTRODUCTION. 
taining round, granular, nucleolated nuclei, and large, 
round or elliptical, transparent cells, with nuclei similar 
to those which lie free in the tissue. 
The integument of the tentaculse is very freely sup- 
plied with nerves from the supra-oesophageal ganglia. 
Taste. If existent, it is probably dependent upon 
nerves distributed within the buccal body, and derived 
from the stomato-gastric ganglia. The structure of the 
lingual lamina precludes any idea of its existence there. 
Sjiell. The presence of this sense is undoubted, 
though there is much discrepancy of opinion as to its 
situation. I have suspected that it probably may be 
placed in the blind sac, or depression, which opens just 
below the mouth. This sac varies in its degree of devel- 
opment in the different genera ; in Linux it is a super- 
ficial depression ; in Yaginulus it extends backwards 
beneath the buccal body for half an inch, is conical in 
shape and yellowish-white in color; in Bulhnus fasciatus 
it extends back, in the excavation of the foot, to the tail, 
and is folded several times upon itself. 
Hearing. The acoustic apparatus consists of a pair 
of transparent, vesicular bodies, placed upon the postero- 
inferior part of the sub-oesophageal ganglia, one on each 
side. They are placed in a depression of the ganglia, 
formed by a separation of the nerve-tubuli as they pass 
from and into the latter, immediately upon the gan- 
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