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displacing the air in spite of the animal. The Pearly Nautilus 
is said to inhabit a depth of from twenty to thirty fathoms. 
The pressure therefore of such a column of water must be very 
considerable, equal indeed to more than six atmospheres. 
Mr. George Bennett, M.R.C.S., F.L.S., through whom Pro- 
fessor Owen obtained the first specimen of the animal of the 
Pearly Nautilus, described by him in 1832, states: “On lay- 
ing carefully open that portion of the shell which contained the 
chambers, it was found to contain water , which of course im- 
mediately escaped.” * 
In 1870 I had an opportunity of opening the chambered 
portion of the shell of a Nautilus umbilicatus , which had been 
preserved, with the animal , in spirits of wine.j The last three 
chambers preceding that occupied by the animal were laid bare 
for a distance equal to half the circuit of the shell-whorl. 
The siphuncle (when the chambers were laid open) was quite 
entire, and sheathed in a thin nacreous investment, which, how- 
ever, attains to considerable thickness near to each septum. 
The chambers contained a large quantity of fluid of which I 
did not specially take note at the time ; but on reading Professor 
Owen’s Memoir, I have no doubt that its presence in this, and 
also in Mr. Bennett’s specimen, was not abnormal (as I had 
supposed), hut in accordance with the natural state of all 
camerated shells, and that it is a misnomer any longer to call 
them 44 air chambers .” 
66 How, then,” Mr. Frederick Edwards inquires (op. cit. p. 1 2), 
“ is the necessary communication between the animal and the 
6 air-chambers ’ maintained, and the vitality of the deserted shell 
preserved?” It has been shown that the siphuncle traverses 
the chambers to the extreme nucleus of the shell, and that it is 
provided with a small artery and a vein ; and we also learn, from 
Professor Owen’s Memoir, that in the Nautilus 4 a delicate 
pellicle, distinct from the tube, is continued over the outer part 
of the testaceous tube, and also over the whole inner surface of 
the chambers.’ 44 May we not, then,” Mr. Edwards adds, 
44 reasonably regard the siphuncle with its artery and vein, and 
the pellicle lining the air-chambers, as the organ destined to 
maintain the vitality of the shell, and feel ourselves justified in 
considering this office to be in fact the primary function of the 
siphuncle ? ” 
Professor Owen, however, does not state that he detected the 
artery and vein beyond a few lines distance from its origin at 
the mantle. He writes as follows : — 
* Extract from Mr. Bennett’s 41 Journal/’ part x., quoted by Professor 
Owen, in his “ Memoir on the Pearly Nautilus,” 1832, p. 7. 
t u British Association Reports,” Liverpool, 1870, p. 128. 
