Miss Agnes Crane — Recent and Fossil Cephalopoda. 489 



succession. The functions of the siphuncle have been variously 

 interpreted. First by Dr. Hooke, in 1696, as serving to admit water 

 to the aerial chambers when the animal was desirous of sinking to the 

 bottom of the sea. The difficulty attendant on the expulsion of the 

 water, and the re-admission of air in the ocean depths, was solved by 

 supposing the Nautilus to be gifted with the power of secreting an 

 aerial fluid at will. But, the fact that the siphuncle only pierces the 

 septa, and has no connexion with the aerial chambers, renders this 

 theory unacceptable. Dr. Buckland ^ held that the siphuncle com- 

 municated with the pericardium, and received a fluid contained 

 therein when the creature was desirous of altering the specific 

 gravity of the shell in order to sink beneath the waves. According 

 to Prof. Keferstein,^ of Gottingen, the Nautilus periodically secretes 

 an aerial gas from the base of its mantle, which is prevented from 

 communicating with the sea water by a special structure, and the 

 gas thus generated causes the animal to move upwards in its shell, 

 and supports its weight when the construction of a new chamber is 

 necessary, the shell muscles advancing gradually and not being 

 abruptly ruptured as supposed by D'Orbigny. The air thus secreted 

 is then inclosed by a nacreous deposit from the mantle, and a new 

 aerial chamber is completed. M. Barrande, who has treated the 

 subject of the functions of the siphuncle, and the progression of the 

 mollusc in the water, in a most impartial and exhaustive manner, 

 in his magnificent memoirs on the Paleozoic Cephalopoda,^ considers 

 the enforced periodic rests, imposed on the creature by Prof. Keferstein 

 immediately after the formation of a new chamber, to be irreconcil- 

 able with the free liberty of movement enjoyed by the other members 

 of the cephalopodous class, and obviates this necessity by assuming 

 that the surface of the mantle endowed with the power of exhaling 

 the aerial gas is also capable of re-absorbing it, and thus the ascent 

 and descent of the Nautilus in the water is entirely under the control 

 of the will of the animal. 



Some authors, however, maintain that the movement of the animal 

 in or out of the shell was sufficient to facilitate its progression in 

 the water, and regard the siphuncle as serving either to attach the 

 animal to its protective covering, or to insure the repair and vitality 

 of the whole of the shell, and a few, as destined merely for the 

 reception and development of the eggs. Others believe that the 

 Nautili live habitually at the bottom of the sea, being only driven to 

 the surface during storms, or when in a dying condition; an argument 

 that is supported by the fact that their chief food appears to consist 

 of the hairy non-swimming brachyurous crabs which live always on 

 the ocean floor. Among those holding this view, and therefore 

 recognizing no necessity for the ingenious theories of Professor 

 Keferstein, and M. Barrande, Dr. Henry Woodward deserves especial 



1 Bridgewater Treatise. Geology. 1836. 



- Bronn's Klassen u. Ordnungen d. Thierreich, III., Malacozoa, 2te Abtheil., 

 p. 1344. 



2 Systeme Silurian de la Boh^me, vol. ii. texts, v. pp. 962 and 1235. Joachim 

 Barrande. Prague, 1877. 



