460 CEPHALOPODA. 



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 tena- 

 cious 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. 



The head of Nautilus (fig. 205) is of a conical form, and of a 

 much denser texture than the analogous part in the Dibranchiate 

 Cephalopods : it is excavated in such a manner as to form a re- 

 ceptacle 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* 

 205, n) with a wrinkled and papillose exterior ; while the sides 

 give off numerous conical and triedral processes (o, o, o) : the in- 

 ferior portion of the cone is thin, smooth, and concave, and rests 

 upon the funnel (z). From 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. 



The lateral processes (o, o, o) are thirty-eight in number, nine- 

 teen on either side, irregularly disposed one upon another, and all 

 converging towards the oral sheath ; but, as the hood itself con- 

 sists apparently of two very broad digitations conjoined along the 

 mesial line, twenty pairs of these lateral appendages may be enu- 

 merated. 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 annulated cirrus or tentacle (Jig. 

 205,^. 212), which is about a line in diameter, and from two 

 inches to two inches and a half in length. In the specimen ex- 

 amined, a few of these 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 



