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Show 1895.] ANATOMY OF NAUTILUS POMPILIUS. 673 two moieties. Of these it is only the right with which the sac of Needham communicates, the left being (as will appear later) connected merely with a peculiar blind sac. The right penial cavity is somewhat semi-pyriform, becoming narrower distally. Its lining is thrown into large smooth glandular-looking rugae, which anastomosing with one another form a kind of raised network with elongated meshes. Outside this lining is the muscular coat about 1*5 m m . thick and largely composed of radial fibres. The muscular layer is traversed by an extensive system of blood-spaces. This is most developed towards the " posterior " end of tbe penis. It forms a distinct layer near the outer surface of the organ, but its spaces also, though less conspicuously, ramify hither and thither in the general substance of the muscle. The left penial cavity is cylindroidal in form, and its diameter only about half that of the right cavity at its widest part. The inner surface of its wall is also thrown into folds ; but these are mainly longitudinal, parallel, and do not anastomose to the same extent as do those of the right cavity. The lining-tissue is of a less deep colour and less glandular-looking; the muscular wall is thinner, and the cavernous layer is also less developed. At its " posterior " end, about the level of the point at which the right cavity becomes continuous with the sac of Needham, the left cavity diverges towards the left side, much as the long axis of the Needham's sac does towards the right, and gradually expands into a flask-shaped sac, in this specimen 6 m m . long by 3 m m. broad. This is rounded off and ends blindly. The inner surface of its wall exhibits faint longitudinal corrugations. It is difficult to believe that this left moiety of the penial apparatus does not represent the reduced fellow of the right moiety, i. e., of the right penial cavity plus the sac of Xeedham. On the left side, however, the rudimentary vas deferens does not communicate with the penial sac, but opens, as is well known, directly into the mantle-cavity. The position of this external aperture corresponds very closely to that of the opening of the vas deferens into the spermatophore sac on the opposite side. The whole arrangement strongly suggests that of the functional male genital duct, only that portion from the ccelomic aperture to its opening into the sac of Needham represents the primitive duct, and that the Needharns sac and the penis are secondarily added structures developed from the adjacent wall of the mantle-cavity. In the young animal, the Needham's sac being not yet expanded, the form and size of the right portion of the apparatus are in almost exactly fhe same condition as is the left in the adult. IV. The Buccal Nervous System. Lankesterl says, in speaking of Nautilus:-" No buccal nervous system has been observed in Nautilus;" and again, " nor has an enteric nervous system been described in this animal." In regard 1 Zoological Articles, p. 142. PROC. ZOOL. Soc-1895, No. XLIII. 43 |