The visceral ganglion of Pecten, etc. 
31 
visceral ganglia are fused forming a single ganglion (fig. 24) situated 
on the posterior adductor muscle with only a very thin layer of connec- 
tive tissue between it and the epithelium. The cerebro-visceral connec- 
tives (fig. 24 e.V. con) enter the visceral ganglion anteriorly and these nerves 
are situated somewhat deeply, running through the tissue of the renai 
organs almost up to the point of entrance into the ganglion. The bran- 
chial nerves leave the sides of the visceral ganglion near the ventral sur- 
face and rather nearer the posterior palhal nerves than the connectives. 
They rise towards the epithelium and are situated therefore very near 
the osphradia, which they innervate. Ali the nerve fibres of the cerebro- 
visceral connectives pass into the centrai mass of the visceral ganglion 
where some run towards and enter the branchial nerve together with 
the fibres from the visceral ganglion itself. No nerve fibres pass there- 
fore to the osphradia or the branchial nerve except from the visceral 
ganglion. 
M y a truncata. This species is particularly interesting. It 
is one of the three figured by Pelseneer in his second paper, and the 
nerves in the neighbourhood of the visceral ganglion are considerably 
different from ali the other lamelUbranchs examined including Ensis, 
which belongs to the same order^). The two visceral ganglia are fused 
forming a single ganglion which lies on the ventral surface of the posterior 
adductor muscle and is separated from the surface epithelium by a very 
thin layer of connective tissue. The cerebro-visceral connectives and 
the branchial nerves enter the ganglion anteriorly, the former being 
situated more deeply and run more in the median line. The fibres of 
the cerebro-visceral connective (fig. 22 c.v.con) on reaching the visceral 
ganglion divide and some turn immediately upwards and run into the 
root of the branchial nerve. The branchial nerve bears at its root a 
thickening which contains numerous ganglion cells, crowded with yellow 
pigment. From this root of the branchial nerve, a small nerve arises 
on the dorsal side and runs along for a considerable distance parallel 
and in dose proximity to the cerebro-visceral connective (fig. 22). 
This nerve was seen by Pelseneer and figured by him, though in 
my sections the nerve runs along with the connective for a greater 
distance before joining the same than his figure indicates. There 
is, therefore in Mya a division of the cerebro-visceral connective taking 
place some distance from the visceral ganglion and a small brauch passes 
1) Pelseneer (1891 pag. 206 footnote) states that the species studied is M. 
arenaria, but the figure is called M. truncata. 
