8o t\)j Subscribers. 



Shortly after the publication of the first part of the Monograph of the Eocene Mollusca, I received 

 a note from Professor Owen, from which the following is an extract : — 



" In reference to the theory of the siphon of the Nautilus, which you attribute to Mr. Wood, I know 

 you will excuse my referring you to a passage (p. 331) of my Lectures on Invertebrata, in which that 

 theory or function of the siphon is plainly though briefly laid down, and I am sure that our excellent 

 Treasurer would be the last person to claim the exclusive credit of the idea, unless his right to it was based 

 on a publication of it prior to 1843. The scrupulous care which characterises your reference to authorities, 

 assures me that if you have overlooked the passage in my Lectures you will be glad to be referred to it." 



Although I had derived much pleasure and instruction from Professor Owen's admirable Lectures, 

 I must confess that the passage referred to had escaped my recollection ; and I greatly regret that this 

 should have been the case, for I should have been glad to have availed myself of the powerful support it 

 affords to the theory I advocated. For the convenience of those Subscribers to whom the Lectures are not 

 immediately accessible, I shall extract the passage to which Professor Owen refers. After noticing 

 Dr. Buckland's theory of the hydrostatic action of the siphuncle, and the objections against it, the 

 Professor advances the opinions to which I have referred in the ' Monograph,' as to the function of the air- 

 chambers being that of a balloon, and as to the mode in which the animal alters the specific gravity of its 

 shell ; and he concludes with the following paragraph, — the one referred to in his letter to me : 



"Whatever additional advantage the existing Nautilus might derive by the continuation of a vascular, 

 organised, membranous siphon through the air-chambers, in relation to the maintenance of vital harmony 

 between the soft and testaceous parts, such, likewise, must have been enjoyed by the numerous extinct 

 species of the tetrabranchiate Cephalopods, which, like the Nautilus, were lodged in chambered and 

 siphoniferous shells." 



It is due to Professor Owen that I should, to the best of my power, repair my omission to refer to this 

 eminently suggestive passage ; and now, having brought it distinctly before the Subscribers, I leave it to 

 them to decide as to whom the credit of the siphuncular theory in question is due. 



F. E. E. 

 July, 1852. 



CORRIGENDA. 



Substitute Sconce for Ilcadon Hill, at p. G5, line 24 ; at p. 70, line 13 j and at p. 7H, line 15. 



*7 



