ON THE ANATOMY OF NAUTILUS POMPILIUS. 207 



"All observers are agreed as to the interpretation of the 

 supra-oesophageal and the two posterior sub-oesopha- 

 geal masses {i.e. (2) and (3)). The disagreement re- 

 lates only to the branchial ganglia, which are regarded 

 by one party as pedal and by the other as cerebral." 

 Pelseneer then goes on to combat the view that the bran- 

 chial ganglion has been derived from the fusion of a downgrowth 

 on each side of the cerebral ganglion. 



While protesting, in passing, against the statement that the 

 supra-cesophageal nerve-mass is formed of "the fused cerebral 

 ganglia," when in reality it represents the primitive nerve-mass 

 out of which "cerebral ganglia" have not yet become segregated, 

 it is (2) the statements as to the " pedal " and branchial ganglia 

 which concern most closely the point under discussion. The 

 one fact of independence of evolution is enough to show that 

 the so-called pedal ganglion of Cephalopods — i.e. the anterior 

 sub-oesophageal nerve-mass of Nautilus, which in the higher 

 Cephalopods has, in accordance with a very general law, become 

 condensed into a definite ganglion, supplying the various organs 

 originally in its neighbourhood — is not in the strict morpho- 

 logical sense the "pedal" ganglion at all. One may then 

 accept with Pelseneer the development of the branchial ganglion 

 by splitting off from this anterior sub-oesophageal nerve-mass, 

 and yet be as completely without evidence as we were before 

 that the structures supplied by it have anything whatever to 

 do with the foot. 



In brief it appears to me that : — the general relations of the 

 parts point undoubtingly to the arms of Cephalopods being 

 processes of the head-region — that all the special evidence 

 brought forward to support the pedal view is either erroneous, 

 of little weight, or is permeated with fallacy — and that it there- 

 fore behoves us in the meantime to unhesitatingly accept the 

 first mentioned'. 



' The forerunner of the hood-tentacle complex of Nautilus (and consequently 

 of the arms of the Dibranchiata) we may probably see still persisting in the 

 similarly innervated and highly sensitive mass which surrounds the mouth in 

 Chiton, 



18—2 



