17(1 
ANODONTA — SENSOR V ORGANS. 
t 
i \ f 
\ 
Fk;. — *• I’rusli *' Sensory 
CelN, highly magnified (after 
Sochaezewer). 
'i'he Stoiiiato-gasti'ic or buccal ganglia, which are so aj)i)areiit in the 
(xastropoda, are not differentiated in Anodonta, hut in correlation 
with the atrophy of the in-otrusihle head region have probably become 
degenerate and intimately fused with the neighbouring cerebro-pleural 
ganglia ; the visceral commissures now giving origin to some slender 
nervous tibrils, which reach the alimentary canal, although splanchnic 
nerves also arise from the chief centres. 
'I'he iSENsoKY organs in our type are not of a highly specialized 
character. 'I'he general surface is, however, richly supplied with a 
mun])er of epithelial sensory cells of the .same character as those 
found in the mollu.sca generally, and, in 
addition, there are some larger cells bearing 
tnfts of sensory hairs and known as “brush” 
cells, which are j)articularly noticeable in 
the Pelecypoda. 'Die perception of tactile 
impressions is most keenly exercised by the 
papilla' or tentacular })rocesses surrounding the branchial siphon, 
but the percei)tion of touch is functionally active and etheient in other 
exposed i)artsof the body. 'I’he labial palps, although enclosed within 
the .shell, have probably a subsidiary tactile function, gnarding the 
oral (iritice again.st the entrance of manifestly unlikely sub.stances. 
'The Auditorv or Mipulibrating organs of Aimloiitd are formed, as 
in lltdl.v, by a pair of small closed ve.sicles or otocy.sts, which in 
Anoddufa are [jlaced near to but 
not in contact with the pedal 
ganglia, and connected by an audi- 
tory nerve to the cerela'o-plenral 
ganglia of their respective sides. 
'I'he otocysts are imbedded in con- 
nective tissue and e:ich surrounded 
by an investing membrane. 'I’he 
walls interiorly of the cysts are 
formed of intermingled .sensory and 
ciliated epithelial cells, which also 
secrete the limpid thud which hlls 
the sacs and within each of which 
one large calcareous concretion or 
otolith is suspended and ke})! in inces.sant motion by the action 
of the vibratile ciliated investment. 'I’he otocysts are, however, not 
Fig. 337. — Otocyst of Anodonta cj'^nca, 
highly magnified (after Simroth). 
and. n. auditory nerve ; c.t.c. connective 
tissue cells ; cu. cuticle or enclosing mem- 
brane ; t'p. ciliated and sensory epithelial 
cells, supported upon cellular tissue ; ot. 
otolith. 
