490 Miss Agnes Crane — Recent and Fossil Cephalopoda. 



mention ' for the lucidity with which he has expressed his opinions 

 in an interesting paper " On the Structure of Camerated Shells," 

 published in the Popular Science Eeview in 1872.^ He there con- 

 tends that the Nautili do not swim, but are sluggish crawling 

 animals, and bottom-feeders, and consequently do not require buoyant 

 shells furnished with air-cells, if indeed the so-called aerial chambers 

 could act as such, liable as they would be to become partially filled 

 with sea- water, which must undoubtedly penetrate by endosmosis 

 through the pores. He denies the possibility of the siphuncle main- 

 taining the vitality of the shell, because it is certainly a non- vascular 

 structure, and there is no connexion between it and those portions of 

 the shell which lie in contact with the mantle, the sole shell -secreting 

 organ in the Mollusca. The divisional septa are regarded as indica- 

 tions of periodical, natural, and reproductive growth,^ and as possibly 

 serving "to shut off the discarded and untenantable" parts of the 

 shell ; and he regards the siphuncle as the remnant of a rudimen- 

 tary or embryonic organ, which attached the animal to the shell in 

 its earliest stages, a function that would well accord with the ex- 

 istence of enormous siphuncles in some of the most ancient fossil 

 forms when the embryonic conditions were probably retained during 

 life. A somewhat similar camerated, or chambered, structure exists 

 in many Gasteropods (Helix, Euomphaliis, etc.), and also in aged 

 oysters and other bivalves, while in some corals a central tube is 

 visible with radiating septa or partitions. Dr. Woodward therefore 

 does not admit the organization of the chambered shells of the 

 Cephalopoda to be an entirely exchxsive structure, but considers it 

 as only a modification of the shell- structure found in other mollusca. 

 The parrot-like jaws of the recent Nautilus are blunt and calcareous 

 at their tips, and similar beaks, called Rhyncholites, formerly regarded 

 as those of fossil birds, occur in all strata associated with the fossil 

 Tetrabranchs, and are now referred to extinct species. "The digita- 

 tions, or lateral processes," thirty-eight in. number, are retractible 

 into eight sheaths, corresponding to the eight ordinary arms of the 

 cuttles. The two dorsal arms unite to form the hood which serves 

 to close the opening at the mouth of the shell. All these numerous 

 arms are unprovided with siackers. There are four gills or branchise, 



1 My attention has been called by Dr. H. "Woodward to a valuable contribution 

 to this subject by Professor H. Govier Seeley, F.G.S., in the report of the British 

 Association for the Advancement of Science, 1864, Bath, Transactions of Sections, 

 p. 100, entitled "On the Significance of the Septa and Siphuncles of Cephalopod 

 Shells; " see also the Quart. Journal of Science, October, 1864. 



* British Association Eeports, Liverpool, 1870, Transactions of Sections. Popular 

 Science Eeview, 1872. See also Note at the end of the present article, p. 499. 



2 On my recently calling the attention of Prof. James Hall, LL.D., to these views 

 as to the significance of the septa in the chambered Cephalopods, that distinguished 

 American palaeontologist, whilst fully admitting the force of the hypothesis of their 

 production by those natural causes, suggested that the fact of the septa being com- 

 posed of three distinct layers of shell-substance, viz. an outer nacreous one, an inner 

 porcellanous one, and a third external nacreous deposit, could hardly thus be ac- 

 counted for. As both the external surfaces were smoothed and polished, apparently 

 by the application of some part of the body of the animal, it was further difficult 

 to conceive how access was obtained to the outer surface of the last formed septa 

 after the animal had once partitioned oflT its body in the manner supposed. 



