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LXXVIII. Observations on Dr. Buckland's Theory of the Ac" 

 tion of the Siphuiicle in the Pearly Nautilus. By Thomas 

 Wright, M.KC.S* 



A LTHOUGH the valuable memoir by Professor Owen 

 -*^ on the Nautilus pompilius has thrown a new and im- 

 portant light upon the history and organization of siphonife- 

 rous cephalopods, still, however, much remains to be learned 

 of the singular structure of this interesting group of the Mol' 

 lusca. From the announcement made by Professor Owen in 

 his article " Cephalopoda," in the Cyclopaedia of Anatomy and 

 Physiology, I was led to expect that Dr. Buckland's Bridge- 

 water Treatise would contain a satisfactory explanation of the 

 action of the siphuncular apparatus of these mollusks. Whilst 

 I admire the tone, talent, and highly popular style of the 

 Bridgewater essay, still I am of opinion that the learned au- 

 thor's theory of the action of the siphuncle is at variance with 

 the facts revealed by the dissection of the animal. On this sub- 

 ject Dr.Buckland observes: "The last contrivance, which I 

 shall here notice, is that which regulates the ascent and descent 

 of the animal by the mechanism of \he Siphuncle, The use of 

 this organ has never yet been satisfactorily made out; even Mr, 

 Owen's most important Memoir leaves its manner of operation 

 uncertain; but the appearances which it occasionally presents in 

 a fossil state supply evidence, which taken in conjunction with 

 Mr. Owen's representation of its termination in a large sac sur- 

 rounding the heart of the animal, appears sufficient to decide 

 this long-disputed question. If we suppose this sac to contain 

 a pericardial Jluid, the place of which is alternately changed 

 from the pericardium to the siphuncle, we shall find in this 

 shifting fluid an hydraulic balance or adjusting power, causing 

 the shell to sink when the pericardial fluid is forced into the 

 siphuncle, and to become buoyant, whenever this fluid returns 

 to the pericardium. On this hypothesis also the chambers 

 would be continually filled with air alone, the elasticity of 

 which would readily admit of the alternate expansion and con- 

 traction of the siphuncle, in the act of admitting or rejecting 

 the pericardial fluid f." In order to estimate the value of this 

 hypothesis, it is necessary to inquire whether the nautilus 

 spends the greater portion of its existence at the bed of the 

 sea, or navigates the surface of its waters. The few authen- 

 ticated instances where this mollusk has been seen at the sur- 

 face, when compared with the thousands of its shells which 



* Communicated by the Author. 



t Bridgewater Treatises, VI. Geology and Mineralogy, vol. i. p. 325. 



