84 



From the inner sides of the cerebro-pleural ganglia 

 two delicate nerves (fig. 27, N. ot.) arise which pass deeper 

 into the tissne and innervate two small bodies, which have 

 a white appearance in dissections. 



These are the otocysts (fig. 27, Ot.), and the Otocystic 

 nerves in Pecten can thus be traced directly from the 

 Cerebro-pleural ganglia. The lower ends of the cerebro- 

 pleural ganglia gradually pass into the cerebro-visceral 

 connectives (fig. 26, Con. cv.). 



The Cerebro-pedal Connectives are very short nerves 

 (fig. 27, Con. cjJ.), which arise about the middle of the 

 inner sides of the cerebro-pleural ganglia and run towards 

 each other and slightly towards the surface. They each 

 bear a ganglionic swelling just before arriving at the 

 pedal ganglia. 



The Pedal Ganglia [G. jy.) lie closely apposed to 

 one another, so that the pedal commissure is so short that 

 it is barely distinguishable. These ganglia are situated 

 outside the foot, and are the nearest to the surface, so that 

 probably they will be the first seen when looking for the 

 cerebro-pleural. Both the cerebral and the pedal ganglia 

 are pigmented yellow, and both have a similar structure, 

 viz., a cortex of ganglion cells with processes passing into 

 a core, made up of nerve fibres. 



From the pedal ganglia, two pedal nerves (fig. 27, 

 N. f.) pass directly into the foot, where they break up 

 into numerous small branches, supplying the muscles. 



The Visceral or Parieto-splanchnic ganglia are 

 completely fused in Pecten to form one large and com- 

 plicated mass (figs. 26, 28, G. sp.). It is the largest 

 ganglion and gives rise to most of the nerves, and this can 

 be accounted for by the fact that, compared with other 

 Lamellibranchs, it is the posterior region of the body that 

 is most developed in Pecten, the anterior with the anterior 



