ON THE ANATOMY OF NAUTILUS POMPILIUS. 201 



VIII. The Morphology of the "Arms" of Cephalopods. 



As Grobben has justly remarked, and as Pelseneer has 

 adopted as text to his paper on the subject "eine der schwierig- 

 sten Fragen in der morphologischen Deutung des Cephalo- 

 podenkorpera bildet die Morphologie der Kopfarme"; and in 

 accordance with this, as well as with its far-reaching interest, 

 the question has attracted from time to time a great amount of 

 attention from morphologists. Regarding the fundamental 

 nature of these organs, two very different views have been 

 brought forward : — 



(1) That the arms of the Cephalopods are processes of 

 the head or circumoral region. 



(2) That they are processes of the foot, part of which 

 has grown up on either side so as to finally surround 

 and almost completely hide from view the head itself. 



To enter in detail into the differences as to minor points in 

 the tenets of the various upholders of these two views seems 

 unnecessary, as this has already been done by others'; and 

 further, because it is proposed to consider the problem here in 

 its most general aspect — as to whether the Cephalopod arms 

 are cephalic or pedal. 



It may be advisable, in the first place, to inquire whether 

 there is anything in the general relations of the parts to support 

 or even suggest the second of these views. In ordinary Cuttle- 

 fishes it is pretty obvious that there is nothing of the kind — the 

 arms form a continuous circle round the buccal mass — one would 

 naturally suppose they belong to the head. It is therefore 

 important to glance at Nautilus, where, as Lankester has well 

 accentuated, " any divergence from the condition obtaining in 

 other forms has possibly, and even probably, a special signifi- 

 cance," and " is not readily to be dismissed as an ' adaptation ' 

 peculiar to that form'," 



^ Cf. especially Pelseneer's admirable summary, •Challenger' Report, 

 Pteropoda. 



5 Quart. Journ. Micr. Science, vol. xxiii. p. 348. 



