266 SPECIFIC GRAVITY REGULATED BY SIPHtJNCLE. 



The universal prevalence of such delicate hydraulic con* 

 trivances in the Siphuncle, and of such undeviating and sys- 

 tematic union of buoyancy and strength in the air-chambers,' 

 throughout the entire family of Ammonites and Nautili, are 

 among the most prominent instances of order and method? 

 that pervade these remains of former races that inhabited 

 the ancient seas ; and strange indeed must be the construc- 

 tion of that mind, which 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 Buck. 



Besides the uses we have attributed to the sinuous ar- 

 rangement of the transverse septa of Ammonites, in giving 

 strength to the shell to resist the pressure of deep water, M. 

 Von Buch has suggested a farther use of the lobes thus 



of the dorsal margin of the shell. This Siphuncle, and also the shell and 

 transverse 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, shows no kind of aperture througii which any fluid 

 could have passed to the interior of the air-chambers. The same con- 

 tinuity 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 supposing that the process of decomposition, in 

 which the oxygen and hydrogen of the animal membrane escaped, was fa- 

 vourable 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 dc* 

 composition. 



