The visceral ganglion of Pecten, etc. 
21 
means of two electrodes made out of ordinary steel needles held together, 
with the points very near each other, by a cork or paraffin wax. The 
result of the application of a weak current to the gangHon was a series 
of violent contractions of the adductor muscle, which were each time 
accompanied by a movement of the velum. The movement of the velum 
when the animai is overturning or at certain other times to be considered 
later, is not the same as the more frequent automatic action seen when 
the animai is swimming, and its action must be governed by several 
sense organs. 
If the palliai nerves are stimulated (best performed on the right 
side, where they enter the mantle in dose proximity to each other) the 
result is also a very definite movement of the velum foUowed by the 
contraction of the adductor. The velar muscles are evidently innervated 
by the palliai nerves which, as we have already seen, contain both sen- 
sory and motor fibres. The cerebral ganglia play but little part in the 
Innervation of the mantle. The naturai supposition would be that the 
orientation was controlied by means of the otocysts. These might, judg- 
ing from their structure, serve two functions, hearing and orientation 
respectively. The experiments made by Fröhlich (1904) on the cephalo- 
poda, where these organs can be more satisfactorily experimented upon, 
ali point to the function being one of orientation. No experimental evi- 
dence has been published so far as I am aware, on the function of these 
organs in the lamellibranchiata, but Dr. Bauer of Naples, who has also 
been making some experiments on the reaction of Pecten to Stimuli, in- 
formed me verbally, that after cutting the cerebro-visceral connectives 
the animals stili turned over, after being placed on their right side. He 
stated however later that this had only happened in one case and he 
had concluded that the injury had been too severe for the others ex- 
perimented upon. The overturning is controlied by the visceral ganglion, 
since it is effected by the mantle and adductor muscle, hence, the cutting 
of the cerebro-visceral connectives should isolate the otocysts which 
are innervated by the cerebral ganglia, and if overturning takes place 
after this severing of the connectives, the otocysts can hardly be the 
determining organs. It may be pointed out in connection with Bauer's 
result, that there is stili a connection left between the cerebral and vis- 
ceral ganglia, by means of the circumpallial nerve, but from Drew's 
(1907) experiments on Ensis there appears to be no evidence of the ganglia 
communicating by this path. 
It is not a difficult Operation to cut the two cerebro-visceral con- 
nectives, once their position is known, but unfortunately they are some- 
