24 
W. J. Diikiü 
nerve centre from the cerebral ganglia, causes violent contractions of 
the adductor muscle, the mantle edge, and the gills. As the ganglion is 
so large and definitely divided, it was thought possible that the areas 
innervated by some of the lobes could be found by experiment. The 
results however were practically the same wherever the ganglion was 
stmiulated, but it must be remembered that the ganglion is small enough 
f or the current to have affected areas other than those directly touched and 
we have already seen that there is a complicated crossing of the fibres in the 
neuropil. If however the dorso-central lobes were stimulated with a weak 
current, there was a most violent series of contractions of the adductor 
muscle, not produced by the same Stimulation of other parts of the ganglion. 
This bears out the histological evidence, that the large ganglion cells in 
these parts are motor in function. Stimulation of the mantle edge, caused 
a contraction of the same, even when it was separated from visceral and 
cerebral ganglia. The circumpallial nerve with its cortex of ganglion 
cells is probably concerned here. If the electrodes were applied at the 
base of the velum, an elevation of the same was the usuai result, and at 
the same time, more especially if the area stimulated was posterior in 
Position, a curious contraction of the gills foUowed. This movement 
is rather interesting since it shows how the branchia also respond to 
irritation of the mantle edge and it is evident that the branchial nerves 
contain motor as well as sensory fibres. The relation of the ganglia which 
are separate, and the two halves of the visceral ganglion is so intimate 
that as Drew found for Ensis, the Stimulation of nerves connected with 
one of the paired ganglia or a nerve arising from one side of the unpaired 
ganglion, causes organs in both sides of the body to respond. 
The Innervation of the Osphradium. 
This sense organ, usually considered an olfactory organ, was dis- 
co vered in the lamellibranchiate moUuscs by Spengel in 1881. A ho- 
mologous organ was known in the gasteropoda previously to this date, 
and Spengel showed the dose relation existing between the two. Lan- 
kester (1883) referred to the organ in an article on the mollusca and 
was the originator of the term osphradium which has since been adopted, 
supplanting the german »Geruchsorgana. He refers to the innervation 
and ascribes this to the visceral ganghon. Spengel's view was rather 
curious and is interesting in the light of present knowledge. It will be 
described when referring to Area, the lamellibranch in which the osphra- 
dium was first discovered. 
