Mr. Garner on the Nervous System of Molluscous Animals. 487 
forms a ganglion (C.) in the substance of the foot, giving many branches to 
this organ. This ganglion in Bivalves is never divided: that it chiefly belongs 
to the foot, and not to the viscera, is proved by its being regulated in size by 
the development of the foot, and being absent when that organ has disap- 
peared. The author could never trace any filaments from it to the viscera. 
It is large in Solen, Mactra, Unio, &c., small in Pecten, Mya and Anomia, and 
absent in Ostrea. It is generally, as in Mactra, situated between the muscular 
tissue and the viscera; more forwards in Cardium echinatum; in Pecten at 
the anterior part of the base; in Pholas superficially at the point. 
In Conchifera then the mouth is surrounded by a ring, of which the lower 
part is double. This ring is, however, very wide, other organs besides the 
mouth being within it. Generally the nervous system is symmetrical; but 
when the animal, as Ostrea, is inequivalve, the nerves going to the branchize 
and mantle in the deeper valve are lengthened and disarranged. In Anomia 
the anterior ganglia are displaced, and the inferior become lateral, from the 
change in the position of the mantle and foot. -The ganglia of Conchifera 
are of an orange colour; in those, however, of which the tissues are trans- 
parent, they are whiter. 
The anterior and posterior ganglia are figured by Poli in many Bivalves ; in 
no instance has he described the inferior one. It is well known that he 
considered these nerves to be lacteals, and the ganglia receptacula chyli, from 
the possibility of injecting their sheaths. 
That the anterior ganglia are the cerebral or sentient lobes of the animal 
appears from this, that the other pairs communicate with them, and not with 
each other. The separate ganglia of each pair are conjoined that their action 
may be consentaneous. The pedal, from its supplying the foot, may be cor- 
rectly termed the ganglion of locomotion; whilst the posterior, supplying the 
branchiz and siphons, may be termed respiratory: but as each pair supplies 
likewise other parts, their functions cannot be purely so limited, though it is 
probable that the subordinate function is derived from twigs they receive from 
the others, incorporated in the connecting nerves. The anterior ganglia in 
the Pecten (fig. 5, B.) are seen to be composed of two portions, one coloured 
and soft, the other fibrous, composed of filaments passing through the gan- 
glia. 
