352 SPECIFIC GRAVITY REGULATED BY SIPHUNCLE. 
of former races that inhabited the ancient seas ; 
and strange indeed must be the construction of 
that mind, which can believe that all this order 
and method can have existed, without the direc- 
tion and aaencv of some commanding: and con- 
trolling Intelligence. 
^riieorij of Von Uucli. 
Besides the uses we have attributed to the 
sinuous arrangement of the transverse septa of 
Ammonites, in giving strength to the shell to 
plates, are converted into thin chalcedony, the pipe retaining in 
these empty chambers the exact form and position it held in the 
living shell. 
The entire substance of the pipe, thus perfectly preserved 
in a state that rarely occurs, shev/s no kind of aperture through 
which any fluid could have passed to the interior of the air- 
chambers. The same continuity of the Siphuncle appears at 
PI. 42, Fig. 3. and in PI. 36, and in many other specimens. 
Hence we infer, that nothing could pass from its interior into 
the air-chambers, and that the office of the Siphuncle was to be 
more or less distended with a fluid, as in the Nautili, for the 
purpose of adjusting the specific gravity, so as to cause the 
animal to float or sink. 
Dr. Prout has analyzed a portion of the black material of the 
Siphuncle, which is so frequently preserved in Ammonites, and 
finds it to consist of animal membrane penetrated by carbonate 
of lime. He explains the black colour of these pipes, by sup- 
posing that the process of decomposition, in which the oxygen 
and hydrogen of the animal membrane escaped, was favourable 
to the evolution of carbon, as happens when vegetables are con- 
verted into coal, under the process of mineralization. The lime 
has taken the place of the oxygen and hydrogen which existed 
in the pipe before decomposition. 
