36 
W. J. Dakin 
10. The orientation of the animai is apparently controlied by the 
otocysts; removal of the abdominal sense organ has no effect on the 
orientation. 
11. The movements of the velum and adductor muscle are coordinated 
and are concerned in the performance of several important functions i. e. 
swimming, orientation, expulsion of reproductive cells. 
12. Removal of the abdominal sense organ has no visible effect on 
the perception of vibrations in the water. The function of this organ is 
probably different from that of the osphradium, and may be the regulation 
of currents in the palliai cavity. 
13. The osphradia in ali the lamelHbranchs examined (with the ex- 
ception of Peden, which has already been referred to) are innervated by 
nervo fibres which arise from the branchial nerve, probably only from the 
ganglion cells forming such a conspicuous cortical layer round this nerve, 
or from those of the visceral ganglion at the base of the branchial nerve. 
The nerve fibres composing the branchial nerve arise chiefly in the vis- 
ceral ganglion, but there are some fibres which come from the cerebro- 
visceral connective. These may pass directly from the latter to the bran- 
chial nerve without touching the visceral ganghon (Mya), they may enter 
the sheath of the visceral ganglion but remain outside the cortex of gang- 
lion cells {Mactra, Spisula), or they may pass through the neuropil of 
the visceral ganglion {Ensis, Pectunculus and other species examined). 
No evidence has yet been produced to show that these fibres from the 
connective have been traced to endings in the epithelium of the osphradia. 
It is quite possible and probable that processes of some of the ganglion 
cells concerned in the Innervation of the osphradium do pass into the 
cerebro-visceral connectives in addition to those which enter the visceral 
ganglion, but it is not easy to follow individuai fibres the necessary dis- 
tance in sections and the evidence appears to show that the visceral 
ganglia are concerned in the innervation of the osphradia. 
