.‘552 SPECIFIC GRAVITY REGULATED DY SIPHUNCLE. 
races that inhabited the ancient seas ; and 
strange indeed must be the construction of that 
mind, Avhich can believe that all this order and 
method can have existed, without the direction 
and agency of some commanding and controlling 
Intelligence. 
Theory of Von JBuch. 
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, shews 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 specifie 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 suppos- 
ing 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 converted 
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. 
