1893. OWEN. 27 



which was known to Aristotle, and had been briefly described by 

 Rumphius. It was, therefore, with peculiar satisfaction that Mr. 

 Owen received an example in alcohol which had been captured, in a 

 dying condition, by his friend and former fellow-student at the College 

 ■of Surgeons, Dr. George Bennett of Sydney, while cruising in the 

 Polynesian seas. The results of his investigations appeared in the 

 " Memoir on the Pearly Nautilus, with illustrations of its external 

 form and internal structure," which, to the keen regret of the author, 

 was not issued from the press until three days after the death of his 

 illustrious master. The animal was shown to be characterised by the 

 presence of pedunculated eyes, calcareous mandibles, like a bird's 

 beak reversed, a crop, gizzard, and liver, four gills, or breathing 

 organs, and by the absence of a branchial heart and ink-bag. It 

 occupied the last and largest chamber of a nacro-porcellanous, many- 

 chambered shell, into the last cell of which it could retract itself and 

 its numerous simple non-aceptabulated arms closing the mouth of 

 the shell by the dorsal arms and by a horny hood-shaped structure, 

 the analogue of the aptychi or double operculum of the fossil 

 Ammonite. A central siphuncular tube pierced all the septa running 

 through all the chambers or so-called " air-cells " which had been 

 occupied by the animal in succession. This siphuncle " subserved a 

 hydrostatic function," enabling the animal to rise to the surface and 

 sink to the bottom, possibly by means of a gas secreted from the 

 mantle. But the author's remark that " much remains to be done 

 before the theory of the chambers and siphuncle can rest on the 

 sound basis of experiment and observation " is still applicable.'-* The 

 order Tetrabranchiata was proposed to receive the recent Naniiliis 

 characterised by the presence of four gills, a many-chambered external 

 shell, and the absence of an ink-bag ; and the fossil Ammonites and 

 their allies were included therein. The Dibranchiata comprised all 

 the two-gilled naked Cephalopods with an internal shell, or pen, and 

 an ink-bag such as the living octopoda, the squids, cuttles, and the 

 fossil Belemnitidae. 



In 1844 Professor Owen resumed the study of fossil cephalopoda, 

 and communicated descriptions and figures of " certain Belemnites 

 preserved with a great proportion of their soft parts in the Oxford 

 Clay at Christian Malford, Wilts." The guard sheath or rostrum, 

 known as the dart or javelin, whence the name Belemnite was origi- 

 nally applied, was described ; the chambered or vertically septated 

 portion was named the phragmacone ; while the presence of an ink- 

 bag, internal shell, muscular mantle, and aceptabulated arms were 

 duly noted, and the fossil molluscs w^ere classed with the recent 



I'l There appears to be no doubt that the deserted chambers of the Natitilus-sheW 

 contain, in the healthy living animal, a gas which serves to lessen the specific 

 gravity of the whole organism . ..." A. certain stage is reached when no new 

 chamber is formed ; with regard to its origin we can only conjecture ; the whole 

 matter is involved in obscurity." Ray Lankester, ninth ed., Ency. Brit., 1S83. 



