TENTACULA OF NAUTILUS. 587 



to the same source from whence we have derived all our information 

 relative to this extraordinary animal. 



(1575.) The head Q 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 

 (ooo): 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 aper- 

 ture 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 i 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. 



(1577.) To the above forty tentacula must be added four others of a 

 different construction, which project immediately beneath the margin of 

 the hood, like antennaB, one before and one behind each eye (fig. 284, r) . 

 These tentacles would seem at first sight to be constructed upon the 

 same principles as the last ; but on examining them attentively, they 

 are found to be composed of a number of flattened circular disks ap- 

 pended to a lateral stem. Yet even all these organs of touch form but 

 a small part of the tactile apparatus of the Nautilus Pompilius ; for the 

 mouth, lodged within the oral sheath, is surrounded with a series of 

 tentacula even more numerous than those appended to the exterior of 

 the head. Around the circular lip (fig. 289, m) which encloses the beak 

 (, o) are situated four labial processes (g g, i i) : each of these pro- 

 cesses is pierced by twelve canals, the orifices of which are disposed in 

 a single but rather irregular series along their anterior margin ; and 



