ON THE ANATOMY OF NAUTILUS POMPILIUS. 205 



endeavour to ascertain whether it is equal to bearing the strain 

 of acting as main support to a view which we have seen to be 

 inherently improbable, on the evidence afforded by gross 

 anatomical relations. And as a preliminary it may be well to 

 look into the general ideas now held and taught by zoologists 

 as to the general character of the Cephalopod central nervous 

 system. 



In the latest text-book of Zoology (Lang, p. 722) one reads, 

 " Das symmetrische Nervensystem aller Cephalopoden zeichnet 

 sich durch die sehr starke Concentration der typischen Mollus- 

 kenganglien, auch derjenigen der Visceralconnective, aus^;" 

 and this I think I may venture to say fairly represents the 

 views held and taught by zoologists generally : that the Cepha- 

 lopod central nervous system consists typically of three pairs of 

 ganglia aggregated round the oesophagus, which ganglia are 

 homologous with the three similar pairs of, say, a Gasteropod. 

 That a certain rough resemblance does exist between the 

 arrangement of the ganglia round the oesophagus of a Di- 

 branchiate Cephalopod and that met with in many Gasteropods 

 may be at once admitted ; but when it comes to be a question 

 of precisely homologizing the individual ganglia in the one case 

 with those in the other, one has to do with a very different 

 matter. Supposing, for a moment, the homology to hold, then 

 one ought to find the resemblance most marked in those 

 Cephalopods which phylogenetically most nearly approach the 

 common ancestral forms of Gasteropods. But what are the 

 actual anatomical facts ? — that in the Nautilus, the most 

 primitive and oldest Cephalopod now existent, such division 

 into three pairs of ganglia is completely absent. And then one 

 might turn to that Gasteropod (I here use the term in its wide 

 sense) which other evidence points to as having similarly to the 

 greatest extent retained such common ancestral conditions — to 

 wit, Chiton. And here again one finds a complete absence of 

 segregation of the central nervous system into its three pairs of 

 ganglia, and in its stead a central nervous system showing in 



' The italics are mine. 

 VOL. VL 18 



