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Show 1895.] ANATOMY OP NAUTILUS POMPILIUS. 679 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 others1; and further, because it is proposed to consider tbe problem here in its most general aspect-as to whether the Cephalopod arms are cephalic or pedal. It m a y be advisable, in the first place, to inquire whether there is anything in the general relations of the parts to support or even to suggest the second of these views. In ordinary Cuttlefishes 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 significance," and " is not readily to be dismissed as an ' adaptation ' peculiar to that form."2 In Nautilus the arrangement of the circumoral lobes and tentacles has been described by Bourne and by Lankester, so that it is unnecessary to go into details. Anteriorly (dorsally) is the large fibrous mass of tissue which forms the hood. Laterally, on each side, is an aggregation of tentacles. Anteriorly (dorsally) the mass of tentacle-sheaths is directly continuous with the hood. O n slicing away the substance of the hood carefully, it is seen that the bases of all the outer tentacles are embedded in it. The appearance of tentacle-sheaths is clue merely to the more or less distinct marking off by superficial grooves of the parts of the mass surrounding each tentacle. Hood and tentacle-sheaths together form a perfectly continuous mass lying anterior (dorsal) to the buccal mass and curving backwards (downwards) on either side of it in saddle-like fashion. In the male this is very obvious, the two limbs of the mass being connected together posteriorly merely by a thin shelf. In the female, however, this bears on its inner side the " inferior inner lobe," which bears on each side a group of tentacles and whose appearance suggests a bilateral origin. The main impression given by the tentacle-hood complex is that of a saddle-shaped structure, situated anterior (dorsal) to the buccal mass-its limbs passing backwards on either side of the latter. The anterior (dorsal) part of the complex here predominates: it is developed less equally all round the buccal mass than in Decapods ; its preponderating part is dorsal. The next point of interest in the gross anatomical relations of the parts lies in the funnel which, according to the upholders of the " pedal " view, is primitively continuous with the tentacle-hood mass. The Funnel.-This is a large tongue-shaped structure attached to the posterior face of the body-to the roof of the mantle-cavity, into which it imperceptibly passes aborally. At its oral end it 1 Cf. especially Pelseneer's admirable summary, ' Challenger' Report Pteropoda. 2 Quart. Journ. Micr. Science, vol. xxiii. p. 348. |