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230 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
accumulates in the more dorsal intrapallal lacunze and 
in the spaces round the adductors. ‘The lacune in the 
contracted foot itself are only potential, and the circulation 
there must be largely confined to that taking place in the 
visceral artery and in the venous lacune round the intes- 
tine. This explanation of the condition of turgescence 
assumes that the quantity of blood contained in the body is 
-sufficient to produce the distension of the parts in question. 
Fleischman has shown that this is the case for Anodonta, 
and the assumption may not unreasonably be made that 
it is the case also in Cardin. 
THE NERVOUS SYSTEM. 
The central nervous system in Cardiwm is constituted 
by the two separate, paired, cerebral ganglia, each of which 
represents the fusion of originally distinct cerebral and 
pleural ganglia; the single median pedal ganglion, formed 
by the fusion of originally lateral and paired pedal ganglia, 
and the single median parieto-splanchnic ganglion also 
formed from originally separate, right and left, ganglionic 
masses. There are two pairs of connectives, the cerebro- 
visceral connectives joining the cerebral and parieto- 
splanchnic ganglia, and the cerebro-pedal which connect 
the cerebral and pedal centres. The whole nervous system 
-is bilaterally symmetrical. 
The cerebral ganglion of each side (fig. 3, Pl. 1., Ga.c.) 
lies quite superficially in the loose connective tissue 
~ between the bases of the labial palps, the anterior dorsal 
wall of the viscero-pedal mass, and the anterior adductor ; 
and is easily exposed by removing the palps close to their 
attachments, and parting slightly the adductor from the 
adjoining body-wall. It is oval in shape and unpigmented. 
The right and left ganglia are joined together by the 
long cerebral commissure (Com.) which runs in the base of 
