600 LECTURE XXIII. 



but the broken portions have been held together by the investing 

 organised integuments, and have been reunited by the deposition of 

 new layers of the fibrous structure peculiar to the guard.* 



The existence of a camerated and siphoniferous structure on this 

 complex and remarkable shell, induced most zoologists to class it with 

 the Ammonites and other more simple chambered shells. Mr. Miller 

 having detected evidence of the internal position of the Belemnite in 

 the exterior characters of the guard, first ventured upon a conjectural 

 restoration of the entire animal f ; and as only the dibranchiate type 

 of Cephalopods vras then known, he placed it in the body of a Cala- 

 mary {Loligo), assigning to the terminal fins the office of clasping the 

 guard and retaining it in its proper position. 



The first evidence that bore directly upon the position of the Be- 

 lemnite in the Cephalopodic class was detected by Drs. Buckland and 

 Agassiz in specimens of Belemnite from Lyme Regis, in which the 

 fossil ink-bag and duct was preserved in the basal chamber of the 

 phragmocone. We must connect with this fortunate discovery the im- 

 portant fact, that remains of an ink-bag have never been met with in 

 connection with any of the more simple or typical forms of chambered 

 shells : we know that the ink-bag does not exist in the recent Nautilus; 

 and it will be shown in the following Lecture that it is present in all 

 the existing Cephalopods which possess more or less rudimental in- 

 ternal shells. I may here anticipate a few remarks on the relations 

 of co-existence of the ink-bag with the organisation of the naked 

 Cephalopods. These highly organised species enjoy active powers 

 of locomotion, which would be incompatible with the incumbrance of 

 a large external protecting shell ; but, to compensate for the want of 

 this defence, nature has provided them with the power of secreting 

 an inky fluid, which, when alarmed, they eject into the surrounding 

 water, and are concealed by the obscurity which they thus occa- 

 sion. The branchial character of the naked Order of Cephalopods is 

 an essential condition of their muscular powers. The presence of an 

 ink-bladder, therefore, in the extinct Belemnites, would have implied 

 the internal position of the shell, even if other proof had been 

 wanting ; and, by the laws of correlation, it implies likewise the 

 presence of the muscular forces for rapid swimming, and the con- 

 comitant conditions of the respiratory, the vascular, and the nervous 

 systems. Connecting, therefore, all these considerations with the 

 detection of the ink-bag in the shell of the Belemnite, I could not 

 hesitate in referring the Belemnites, and likewise the Spirula, on 

 account of the ascertained internal position of its shell, to the Di- 



* Duval- Jouve, Memoire sur les Belemnites. 4to. 1841. pi. x. 

 t Geological Transactions, N.S. vol. ii. p 45. pi. ix. 1823. 



