504« Mr. Wright*s Observations on Dr. BuQkhmVs Theory 



are annually imported into Europe, affords prima facie evi- 

 dence that the nautilus is an inhabitant of the silent depths 

 of the sea ; but when we inquire whether the organization of 

 the animal sanctions this inference, we discover in its ana- 

 tomy peculiarities of structure to adapt it to such a mode of 

 life, the function of which it is impossible to mistake. The 

 number and rudimentary condition of the cephalic append- 

 ages, the presence of a ligamento-muscular disc analogous to 

 the foot of gasteropods, and adapted as a locomotive instru- 

 ment for creeping along the bottom, the simple structure and 

 pedunculated character of the eyes, the dense calcareous na- 

 ture of the jaws, the structure of the digestive organs, but above 

 all the contents of the stomach, which consisted, according to 

 Owen, of the remains of a species of crab*, constitute an as- 

 semblage of characters which enable us to pronounce the 

 manor of this mollusk to be the bed of the sea, where it preys 

 upon Crustacea and other invertebrata. But the nautilus has 

 been seen occasionally at the surface of the water, and the 

 question naturally arises, what are the conditions necessary to 

 accomplish its ascent and descent ? 



1st. That the animal should be capable of rendering itself 

 specifically lighter and heavier than the ambient ele- 

 ment. 

 2nd. That the mechanism by which this act is accomplished 

 should be under the control of its will. 

 Now, Professor Buckland's theory allows only of a change 

 of place in the adjusting fluid, from the pericardial cavity 

 into the siphuncle, and vice versa \ consequently the specific 

 gravity of the entire aiiimal remains the same. The accom- 

 panying outline f, from Owen's dissections, shows the relative 

 position of the internal organs : a a is the enveloping fleshy 

 mantle dissected off to expose hb^ the branchiae floating in 

 c, the branchial chamber for the reception of the water ; d 

 is the heart with its large vascular canals surrounded by clus- 

 ters of glandular follicles, e e. The capacious pericardium 

 ff is laid open to show its boundary and relation to the cen- 

 tral organs of the circulation ; it is partially divided internally 

 by thin muscular septa, gg. 



From the posterior wall of this musculo-membranous bag 

 there proceeds a canal, or siphuncle, 5 5, destined to traverse all 

 the chambers of the shell: the arrow shows the direction of this 

 aquiferous tube. Anteriorly the pericardium communicates 



• Art. Cephalopoda^ Cyclopaedia of Anatomy, p. 531. 



f For splendid figures of the animal and shell o^ the Nautilus pmnpiiiusy 

 consult Dr. Buckland's 31st and 34th plates; also Prof, Owen's invaluable 

 memoir. 



