INTRODrCTIOX. 
Xlll 
emanating from the animal. More conclusive evidence on this 
head is furnished by Professor M. Yrolik, of Amsterdam, who 
(assisted by M. van Breda) dissected a Xantilus' and found that the 
chambers of the shell contained gas^. Several chambers were 
opened under water and the gas was collected ; it proved to contain 
a larger proportion of nitrogen than the atmospheric air. M. van 
Breda, who analyzed the gas, could not detect in it the slightest 
trace of carbonic acid. There is no doubt that upon this authority the 
chambered shells of Cephalopods have been called “ air-chambers.” 
Owen has expressed the opinion that the vacated chambers of the 
XautUus served to reduce its specific gravity so as to enable it 
to rise from its habitual position at the bottom of the sea, “ such 
vertical movements being executed, like the horizontal ones, by 
means of the hydrostatic mechanism worked by the muscular 
forces of the mantle and funnel 
Dr. H. Woodward considers the term “ air-chambers ” misap- 
plied, because in a specimen of Xautilus mnhilicatus (“ preserved 
with the animal in spirits of wine ”) opened by him he found that 
the chambers, three of which he laid bare, contained “ a large 
quantity of fluid This was also the case with the specimen 
collected by Mr. George Bennett, which furnished the subject of 
Owen’s classical memoir. 
It is much to be regretted that recent opportunities of setting 
this question at rest should apparently have been neglected. 
Turning our attention now to the order of succession of the 
principal types of fossil Cephalopods, it appears that those having 
the most simple construction were the most abundant and persistent, 
* Ann. Mag. Nat. Hist. vol. xii. 1843, p. 173. 
^ Huiley states that he has observed gas in the pores of the internal rudi- 
mentary shell of Sepia, which “ has necessarily been liberated by the tissues 
which secrete the shell, and not derived from any external source ” (Lankester, 
in Encyclop. Britannica, 9th ed. vol. xvi. 1883, p. 671). Professor Lankester 
informs me in a letter that reference is here made to the newly hatched young, 
and that he can confirm Huxley’s statement from his own observations. 
® Owen, “ On the relative positions to their Constructors of the Chambered 
Shells of Cephalopods,” Proc. Zool. Soc. Nov. 1878, p. 955. 
* “On the Structure of the Shell in the Pearly Nautilus,” Brit. Assoc. 
Rpport, Liverpool, 1870 ; Biology Sect. p. 128. 
Dr. Woodward tells me that many dozens of specimens of the newly imported 
shells of Nautilus, examined by him at the Docks, were, when shaken, found to 
contain fluid within their chambers, j ust as in the camerated shell of the Water- 
Spondylus (<9. varians). 
