ANODONTA — NERVOUS SYSTEM. 
1G9 
The Pleuro-pedal connectives, wliicli have been hitherto considered 
to be a characteristic peculiar to the Gastropoda, are present in onr type, 
but fused with the cerebro-pedal connective, forming the composite 
or compound neiwous -cord, dis- 
tinguished as the cerebro-pleuro- 
pedal connective. 
The Visceral, Osphradial, or 
Parieto-splanchnic ganglia are the 
largest in the whole system, and 
are really composite ganglia formed 
by the fusion of several ganglionic 
masses, the more or less com])lete 
conjunction of the constituent 
ganglia being coi’related with the 
greater or less degree of fusion 
which the bilateral gills have under- 
gone ; these ganglia are supeidicially 
placed, and merely covered by 
the tegumentary epithelium ; they 
innervate the branchire, the siphons and the siphonal chamber, the 
posterior adductor, the posterior part of the mantle, and the heart, 
which is supplied by a nerve passing around the adductor. The nerve 
trunks from the visceral ganglia innervating the posterior portion 
of the mantle and those from the cerebro-pleural ganglia, which 
innervate the anterior part, fuse or anastomose together and form 
a marginal pallial nerve with an intricate plexus of ramifying nerve 
fibrils and small ganglionic enlargements. 
The Cerebro-pleural connective is lost owing to the intimate fusion 
of the cerebral and pleural ganglia, and I therefore regard the long 
nervous cords joining the cerebro-pleural and the visceral ganglia, as 
commissures, and as really joining the pleural constituents of the cere- 
bro-pleural ganglia with the visceral centre ; they run close together 
between the anterior protractor and retractor muscles and the anterior 
end of the pericardium, and traverse the inner surface of the renal 
organs ; they then diverge, passing outside the posterior retractors, and 
proceed to join the visceral ganglia. At the point of divarication of each 
commissure there is a ganglionic enlargement, wdiich Moquin-Tandon 
considered to be a genital and Huxley a subsidiary visceral ganglion. 
Fig. 33.5. — Transverse section through 
anterior region of A^iodonta cygnca to show 
the relation of the mouth and labial palps and 
the position and arrangement of the cerebro- 
pleural and pedal ganglia (after Howes). 
a. ad. anterior adductor ; c.c. cerebral com- 
missure ; C’PLg. cerebro-pleural ganglia ; 
C'Pl’p.c. cerebro-pleuro-pedal connective ; f. 
foot ; l.p. labial palps ; in. mouth or oral aper- 
ture ; p.g. pedal ganglia. 
