626 



CEPHALOPODA. 



Fig. 213. 



have a similarrelation of subserviency to the loco- 

 motive and prehensile faculties of the animal. 



Among the Vertebrates traces of organs corre- 

 sponding to these cephalic feet are met with 

 principally in the class of Fishes, in the form 

 of tentacles developed from the lips ; and 

 Schultze, a learned German Naturalist,* has 

 indicated the close affinity -which the Cyclo- 

 stomous Fishes bear, in this respect, to the 

 Cephalopods; in one genus, viz. Gastro- 

 branchus, or Myxine, eight free filaments are 

 extended forwards from the circumference of 

 the funnel-shaped orifice of the mouth, repre- 

 senting the eight ordinary arms of the Cepha- 

 lopoda Dibranchiata, but arrested in their de- 

 velopment because of the pre- 

 ponderating size of the caudal 

 extremity of the body, which 

 now forms the sole locomotive 

 organ. The expanded sucker 

 anterior to the jaws of the 

 Lamprey may, in like manner, 

 be considered to represent the 

 united bases of the cephalic 

 feet of the class under consi- 

 deration. 



In the Nautilus the cephalic 

 organs of prehension and loco- 

 motion consist of slender sub- 

 cylindrical annulated tentacles, 

 which are sheathed and retrac- 

 tile, (fig. 213,) like those of 

 some of theGasteropodousMol- 

 lusks, as Doris, Thethys, and 

 Tritonia. Here, however, they 

 astonish the observer by their 

 unexampled number, sur- 

 rounding the mouth in suc- 

 cessive series, and amounting 

 to little short of a hundred. 

 These tentacles are divided into 

 three kinds, according to their 

 situation, viz. ' brachial or 

 digital/ ' ophthalmic,' and 

 ' labial : ' the latter being 

 again subdivided into ' ex- 

 ternal' and ' internal.' 



The brachial tentacles are 

 forty in number, and are sup- 

 ported by short conical trihe- 

 dral hollow processes or digita- 

 tions, (e, e,jig. 205,) of which 

 the two superior or dorsal ones 

 are conjoined and dilated into 

 a muscular disk covering the 

 whole upper part of the head, 

 (fig'fig- 205;) the remaining 

 thirty-eight are disposed ir- 

 regularly, nineteen on either side, one over- 

 lapping another, and all directed forwards, con- 

 verging towards the orifice of the oral cavity, 

 in which the jaws and mouth are concealed. 

 The longest of these digitations, when its free 

 extremity only is measured, does not equal one 

 inch ; but externally they appear longer, be- 

 cause they adhere for some way to the sides of 

 the head. The digitations present no trace of 



* Meckel Archiv. fiir Physiologic, B. iv. p. 338. 

 1818. 



Digitation and 



Tentacle, 

 Nautilus Pom- 



jiilius. 



acetabula or suckers, but are perforated at the 

 extremity by a canal (a, a, jig. 213,) which is 

 continued far into the substance of the head to 

 near the cerebral ring ; the tentacle (i) which 

 is lodged in this canal, is consequently longer 

 than the digitation fiom which it is protruded. 



The labial tentacles, forty-eight in number, 

 extend from orifices situated on the anterior 

 margins of four broad flattened processes, 

 arising from the inner surface of the oral 

 sheath opposite the base of the mandibles. 

 Two of these processes (a, a, fg. 219) are 

 superior, posterior, and external in situation ; 

 the other two, (b, b,fig. 219,) which are smaller, 

 are inferior, anterior, and more immediately 

 embrace the jaws, and they are connected to- 

 gether by a lamellated organ (c, jig. 219), after- 

 wards to be described. Each of these ' labial' 

 processes is pierced by twelve canals contain- 

 ing the tentacles in question : they differ from, 

 the digital tentacles only in relative size, and 

 in being of a softer and more delicate texture. 



The ophthalmic tentacles seem more ex- 

 pressly designed as instruments of sensation ; 

 they do not possess the strength requisite for 

 prehensile purposes, and are not situated con- 

 veniently for locomotive actions; they are four 

 in number, and project laterally one before and 

 one behind each eye, involuntarily reminding 

 the observer of the antennae in Crustacea, &c. 

 At first sight they seem annulated like the 

 brachial and labial tentacles ; but upon a closer 

 examination, they are found to consist of a num- 

 ber of flattened circular disks closely packed 

 upon a lateral stem, a structure which is sin- 

 gularly analogous to that of the antennae of 

 the Lamellicorn Beetles. In this respect, how- 

 ever, the Pearly Nautilus does not stand alone 

 in the Molluscous series, the retractile tentacula 

 of the Doris present a very similar structure. 



The fibres of the dense musculo-ligamentous 

 sheath (d, d, jig. 219), which incloses the man- 

 dibles and supports the eyes and digital pro- 

 cesses, arise from the whole of the anterior 

 and outer part of the cartilaginous skeleton 

 above described. They were so densely in- 

 terwoven in the specimen we dissected as to 

 preclude the possibility of ascertaining their 

 exact course or arrangement. 



The large lateral muscles of the funnel come 

 off principally from the infundibular processes 

 of the internal cartilage. There are also two 

 small round and distinct muscles designed to 

 draw the funnel closer to the head, they pass 

 to their insertion through canals excavated in 

 the sides of the funnel. 



The fleshy masses which proceed backwards 

 from the posterior part of the skeleton are the 

 two great muscles (b, b, /?g.231,) which attach 

 the Nautilus to its shell. These are inserted 

 by obliquely truncated flattened extremities 

 into a layer of horny substance which is 

 closely adherent to the inner surface of the 

 sides of the last chamber of the shell at a little 

 distance from the septum forming its base : 

 where, in recent specimens, these impressions 

 are always to be plainly seen. The part which 

 passes through the perforations of the septa is 

 not a muscular or tendinous chord, as has been 

 conjectured, but a weak membranous tube, 



