(1569). The ganglia connected with the inferior aspect of the supra-oesophageal mass form two distinct collars embracing the oesophagus, - an arrangement of which we have already met with an example in Clio borealis among the Pteropod Mollusca. In Nautilus, the anterior ring of nervous substance, which no doubt ought rather to be considered as an agglomeration of ganglia than as a simple ganglionic mass, gives off nerves, 1st, to the ophthalmic tentacles (fig. 291, 5); 2ndly, to the digital tentacles (6); 3rdly, there arises, from near the ventral aspect of the ganglionic collar, a pair of nerves (7), each of which soon dilates into a large ganglion (8), from whence are derived the nerves of the internal labial tentacles (9) and also other gangliform nerves (10), distributed to what Professor Owen regards as the olfactory apparatus; lastly, the anterior collar gives off nerves (11) which penetrate the muscular integument and supply the infundibulum.

* Descriptive and Illustrated Catalogue of the Physiological Series of Comparative Anatomy contained in the Museum of the Royal College of Surgeons of England, vol. iii. part 1. p. 187.

1 Cyclopaedia of Anatomy and Physiology, art. Cephalopoda.

(1570). In the Dibranchiate Cephalopods, the nerves derived from that portion of the brain that may be regarded as analogous to the anterior collar of Nautilus supply the locomotive sucker-bearing arms, the labial apparatus, and also the auditory organs (fig. 294, c, d); but the latter have not been found to exist in Nautilus Pompilius.

(1571). There is no possibility of doubting that the above nerves, distributed as they are to the complex sensitive tentacula connected with the head and parts of the mouth, represent the fifth pair in the Vertebrata - their general distribution and semi-ganglionic character being, ceteris paribus, precisely similar; so that those portions of the brain of vertebrate animals from whence the trifacial and auditory nerves originate may reasonably be compared with the anterior sub-cesophageal collar of the Cephalopoda.

(1572). The posterior subcesophageal ganglionic ring (fig. 291, 4) may be compared to the medulla oblongata of quadrupeds. In Nautilus it gives origin, 1st, to numerous nerves (13) which, after a short course, plunge into the muscular parietes of the body, to which they are distributed; 2ndly, to two large cords (14) which terminate by becoming gangliform (16), and supply the branchial apparatus and the viscera - thus representing the par vagum in their distribution, and in like manner communicating with branches apparently corresponding with the sympathetic nerves that are spread out over the heart and ramifications of the vascular system; lastly, slender nerves, allied to the sympathetic, accompany the vena cava into the abdomen.

(1573). Such being the arrangement of the principal nervous ganglia and the general distribution of the nerves, we must now turn our attention to the instruments of sensation possessed by these comparatively highly-gifted animals; and these, as we shall soon perceive, are in all respects correspondent, in the perfection of their structure, with the exalted condition of the brain, and, from their peculiar organization, highly interesting to the physiologist.

(1574). The sense of touch, as might naturally be expected, resides principally in the tentacula, or feet, as they are generally termed, placed around the mouth, and forming, as we have already seen, instruments of locomotion as well as prehensile organs. In the Dibranchiate Cephalopods these tentacula are armed with the tenacious suckers described in a former page; but in the Nautilus they are so peculiar, both in structure and office, that a more elaborate description of them becomes requisite in this place, for which, of course, we are necessarily indebted to the same source from whence we have derived all our information relative to this extraordinary animal.

(1575). The head of Nautilus (fig. 284) is of a conical form, and of a much denser texture than the analogous part in the Dibranchiate Ce-phalopods: it is excavated in such a manner as to form a receptacle or sheath, into which the mouth and its more immediate appendages can be wholly retracted, and so completely concealed as to require the aid of dissection before they can be submitted to examination. The orifice of this great oral sheath is anterior, its superior parietes being formed by a thick triangular hood (fig. 284, n) with a wrinkled and papillose exterior, while the sides give off numerous conical and trihedral processes (o o o): the inferior portion of the cone is thin, smooth, and concave, and rests upon the funnel (i.) Prom the disposition of the hood, and the tough coriaceous texture of its substance, it is evident that this part is calculated to perform the office of an operculum by closing the aperture of the shell when the body of the animal is retracted.

(1576). The lateral processes (o o o) are thirty-eight in number, nineteen on either side, irregularly disposed one upon another, and all converging towards the oral sheath; but as the hood itself consists apparently of two very broad digitations conjoined along the mesial line, twenty pairs of these lateral appendages may be enumerated. There is not the slightest appearance of acetabula, or suckers, upon any of these cephalic appendages; but their exterior surface is more or less rugose: each is traversed longitudinally by a canal, in which is lodged an annu-lated cirrus or tentacle (figs. 284, 291), which is about a line in diameter, and from 2 inches to 2 1/2 inches in length. In the specimen examined, a few of the cirri were protruded from their sheaths to the extent of half an inch, but the rest were completely retracted, so as not to be visible externally; and on laying open some of the canals, the extremities of several were found as far as a quarter of an inch from the aperture; so that they appear to possess considerable projectile and retractile powers.