1895.] ANATOMY OF JfATJTlLUS POJIPILIUS. 681 



are pedal in their nature, was based upon three different sets of 

 evidence — to vvit, those derived from 



(1) Their ontogenetic development ; 



(2) Their innervation ; 



(3) Their homology with the sucker-bearing processes of the 

 larval Pneumoderma. 



Of these (3) derived its force from the supposed pedal nature of 

 the sucker-bearing appendages. However, it has now been satis- 

 factorily shown ' that they are purely cephalic, and therefore this 

 argument, if it be argument at all, tells precisely in the opposite 

 direction. At present, therefore, the view that the Cephalopod 

 arms are parts of the foot rests upon (1) and (2). In regard to 

 (1), however, although it must be admitted that the facts of embry- 

 ology do tend to bear up the view that the crown of arms is formed 

 by an upgrowth from each side of the foot, it must be borne in 

 mind how extremely unreliable any evidence, as to topographical 

 relations, must be which is based on the phenomena exhibited in 

 the development of enormously yolk-laden eggs. Therefore it 

 appears that the only one of the three classes of evidence adduced 

 above which can be considered of real weight, is that resting upon 

 the innervation of the parts under consideration, and that this 

 opinion is shared by other w-orkers, is shown by its tendency 

 in more recent wTitings to supplant the evidence derived from 

 embryology. It appears, therefore, not inadvisable to submit 

 this portion of the evidence to a short critical examination, to 

 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 ana- 

 tomical 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 seJir starhe Concentration der typischen MollusJcen- 

 ganglien, 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 Cephalopod 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 Dibranchiate 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 phylogeneticaUy most nearly 



1 ' Challenger ' Keports : Pteropoda, Anatomy, p. 39. 

 * The italics are mine. 



