THE MORPHOLOGY OF THE MOLLUSCA. « 15 
points unhesitatingly to the opposite conclusion. Von 
Erlanger has shown that in Azthynza as well as in Paludina 
the abdominal ganglion develops as an ectodermal pro- 
liferation of the floor of the mantle-cavity, ze., that the 
ganglion is essentially a dorsal ganglion. Its final situation 
on the course of the sub-intestinal nerve-loop is rendered 
possible by the fact that its connectives with the visceral 
ganglia are not delaminated from the ectoderm, as are the 
ganglionic pleuro-visceral cords of Chzton, but are mere 
fibrous outgrowths from the ganglia themselves. Embry- 
ology is thus in complete accord with the views which have 
been maintained in the earlier part of this paper as to the 
homologies and origin of the visceral nervous system in 
Mollusca. 
The palhal and visceral commussures in Cephalopoda. 
—It has long been known (Hancock) that in many Cepha- 
lopoda the stellate ganglia on the pallial nerve-cords are 
connected with one another above the gut by a transverse 
commissure. Is this commissure a relic of the pallio-visceral 
nerve-ring of the Amphineura and homologous with the 
pallial ring of Zoé¢za, or is it merely a secondary connection ? 
In Stirula a remarkable arrangement of the pallial 
commissure has been recognised by Huxley and Pelseneer 
in their recent memoir (12). The commissure is not in 
this case a straight transverse band, but consists of two 
curved cords which arise from the right and left stellate 
ganglia respectively, and at their junction in the median 
line of the body give off a median pallial nerve which runs 
for a short distance forwards, and then passing over the 
anterior margin of the shell—which is, of course, internal— 
becomes recurrent and runs along the part of the mantle 
contained within the last chamber of the shell. Pelseneer is 
thus led to regard the commissure with its median nerve as 
formed by the two original pallial nerves fused together. 
The connection between the stellate ganglia having thus 
arisen in the primitive Dibranchiates (apparently in con- 
