CEPHALOPODA. 583 



masses which, on the one hand, attach the soft parts to the shell, and, 

 on the other, connect the head to the body, we may conclude that 

 the funnel is the principal organ of natation, and that the Nautilus is 

 propelled, like the Octopus, by a succession of jerks occasioned by 

 the reaction of the respiratory currents upon the surrounding water. 

 The orifice of the funnel is guarded by a valve {fig. 214, i!). 



The retraction of the tentacula is done by longitudinal fibres, the 

 elongation by transverse ones. These are not, however, disposed in 

 circular or spiral series, so as to attenuate and lengthen the tentacle 

 by a general compression, but present a more complex disposition 

 by which they diminish the transverse diameter without com- 

 pressing the central nerve. The transverse fibres {fig. 216, a) arise 

 in numerous and distinct fasciculi from the dense cellular tissue 

 {h\ surrounding the nerve in the centre of the tentacle {d\ and 

 radiate at equal distances to the circumference ; they divide and sub- 

 divide as they diverge, and also send off lateral fibres, which form a 

 delicate network in the interspaces of the rays, especially at the 

 angles : the meshes include the longitudinal fasciculi, the cut ends of 

 which are shown at c. 



The mechanical arrangement of the contractile fibres is very 

 similar to that of the complex muscles described by Cuvier in the 

 proboscis of tlie elephant. The attenuation and elongation of this 

 brobdignagian tentacle must be effected without compressing the 

 central breathing tubes, and transverse fibres accordingly radiate 

 from the dense ligamentous tissue which surrounds them : the same 

 prospective contrivance is manifested to prevent the compression of 

 the nerves and vessels in the muscular system of the ninety probos- 

 cides of the Nautilus. 



For the special account of the myology of the Nautilus, which in- 

 cludes the muscles of the oral sheath and its digitations, of the labial 

 processes and mouth, and of the infundibulum, those for adhesion to 

 the shell, those of the mantle, those of the tongue, the fibres of the 

 tunic inclosing the liver and stomach, and the muscles of the organic 

 system, I must refer to the published monographs on the anatomy of 

 this animal.* 



The principal masses of the nervous system of the Pearly Nautilus 

 {fig. 215.) are concentrated in the head. The super-oesophageal 

 part, or brain (a), presents the form of a short, thick, transverse, 

 round chord or commissure, connected at each extremity with three 

 ganglionic masses. The middle and superior of these (6) supplies the 

 eye and the inferior hollow tentaculiform organ : the anterior and 



* CCCLXXXVII. & CCCLXXXVllI. 

 r r 4 



