26 
W. J. Dakin 
tory evidence has been brought forward. There is also a statement of 
Freidenfelt (1897) to the effect that the fibrillae of the osphradial 
epithehum in Änodonta belong to ganglion cells of the branchial nerve. 
One might expect the osphradium in a lameUibranch hke Pecten 
to be innervated by the visceral ganglion, for the adductor muscle and 
mantle, organs which respond first to warning Stimuli are both innervated 
by this ganglion, and it would be necessary therefore, if the osphradium 
was supphed solely by nerves from the cerebral ganglion for the nervous 
impulse to pass through the long cerebro-visceral connective to the cerebral 
ganglion and then back again to the visceral ganglion from which the 
motor nerves would pass it on to the muscle, and this before the response 
to the Stimulus could be effected. Or again after what has been disco- 
vered concerning the distribution of the nerves it would not be irrational 
to suspect the nerve cells connected with the osphradium of having nerve 
endings in both cerebral and visceral ganglia. 
It has been already shown that in Pecten the Innervation of the 
osphradium is rather complicated and like the visceral ganglion probably 
unique. The length of the nerves connected with the sense organ i& 
due to the fact that the osphradium is situated at some distance from 
the visceral ganghon and is not confined to a narrow region ab ove the 
branchial nerve. In most of the other species examined the branchial 
nerve runs close to the surface and the course of the osphradial fibres 
\s not so obvious. Serial sections have been used in all cases and these 
were cut both in the plane of the ganglion and sagittal. The following 
species of LameUibranchiata have been examined. 
Order Eleutherorhabda (= Filibranchiata + Pectinacea). 
Sub-Order Arcacea. Fam. Arcidae. Area noae, Pectunculus 
glycimens, 
Sub-Order Mytilacea. Fam. MytiMdae. Lithodomus. 
Sub-Order Pectinacea. Fam. Pectinidae. Pecten maximus^ 
P. jacobaeus. 
Order Synaptorhabda (= Eulamellibranchiata + Ostraeacea). 
Sub-Order Ostraeacea. Fam. Pinnidae. Pinna noUUs. 
Sub-Order Tellinacea. Fam. Mactridae. Mactra stultorum, Spi- 
sula solida. 
Sub-Order Veneracea. Fam. Veneridae. Venus casina, Tapes 
pullastra. 
Sub-Order Cardiacea. Fam. Cardiidae. Cardium edule. 
