CEPHALOPODA. 465 



cicatrix, presence of a pro-sipho, and character of the Aptychus, make it possible 

 that the Ammonoidea belong to the Dibranchiata. 



II. Dibranchiata. Shell chambered and partially external (Spirula] ; or chambered 

 with a guard, and internal (Belemnitidae); plate-like and internal (Decapoda) ; or absent 

 (Octopodd). An external calcareous but not chambered shell in the female Argon- 

 auta Argo (Octopodd) formed by a pair of arms. Foot surrounding mouth produced 

 into sucker-bearing arms. Lobes of siphon fused. Eyes large ; retinal chamber 

 closed by a lens ; no osphradia. A single pair of ctenidia ; a pair of auricles and 

 branchial hearts; and of nephridia into which the viscero-pericardial sac opens. 

 Two vasa deferentia in Eledone moschata ; two oviducts in Ommastrephes, and in 

 Octopoda j otherwise genital duct unpaired. An ink-bag. 



(1) Decapoda. Ten arms; one pair much elongated; suckers pedunculate, 

 and strengthened by a horny ring ; lateral body fins. Nidamental glands usually 

 present. Belemnitidae extinct ; Mesozoic (Trias to Chalk) ; ? Tertiary. Oegopsidae, 

 cornea perforate, e. g. Ommastrephes ; Myopsidae, cornea closed, e. g. Sepia, Loligo. 

 Spirulidae, a chambered skull ; Spirula Peronii, warmer seas. 



(2) Octopoda. Eight arms, with a more or less developed inter-brachial mem- 

 brane. Eyes with a sphincter-like lid. Cirrhoteuthidaei. Philonexidae, e. g. Ocy- 

 thoe, Argonauta ; Octopidae, e. g. Octopus, Eledone. 



Cephalopoda, Keferstein, Bronn's, Klass. und Ordn. des Thierreichs, iii. 2, 

 1862-66; Hoyle (Systematic and distribution), Challenger Reports, xvi. 1886. 



General account of Nautilus, Ray Lankester, Encyclopaedia Brit. (ed. ix.), 

 xvi. p. 670 et seqq. Osphradium and genital ducts, Id. and Bourne, Q. J. M. 

 xxiii. 1883. Male and female ; differences, Bourne, Nature, xxviii. 1883. 



Dibranchiata. Skin; chromatophores ; suckers, Girod, A. Z. Expt. (2), i. 1883; 

 ii. 1884. Chromatophores, Blanchard, C. R. xcvi. 1883 (A. N. H. (5)xi.); Phy- 

 siology, Krukenberg, Vergleich. Physiol. Studien, i. i. 1880. Suckers, Niemiec, 

 'Les ventouses,' &c., Recueil Zool. Suisse, ii. 1885. Ctenidia, development and 

 structure, Joubin, A. Z. Expt. (2), iii. 1885. Nervous system of Ommastrephes, Han- 

 cock, A. N. H. (2), x. 1852. Eye, Carriere, ' Seh-Organe der Thiere,' Leipzig, 

 1885; Grenacher, Abhandl. Nat. Gesellsch. Halle, T xvi. 1884; cf. note, p. 452, ante; 

 of Procalistes, Ray Lankester, Q. J. M. xxiv. 1884. Digestive organs (histology), 

 Li von, Journal de 1'Anat. et Physiol. xvii. 1881. Pancreas, Vigelius, Z. A. iv. 

 1884; Biol. Centralbl. ii. 1882-83; Physiology, Bourquelot, A. Z. Expt. (2), iii. 1885. 

 Ink-bag, Girod, A. Z. Expt. x. 1882. Excretory organs and pericardial glands, 

 Grobben, Arb. Zool. Inst. Wien, v. 1884; Vigelius, Archiv. Nederland. f. Zoologie, 

 v. 1879-82 ; Solger, Z. A. iv. 1881. Sex organs, Brock, Z. W. Z. xxxii. 1879; Id. 

 Males of Sepioloidea, Z. W. Z. xl. 1884. 



Various points relating to anatomy, &c., Brock, 'Phylogeny,' &c., M. J. vi. 1880; 

 Id. Z. W. Z. xxxvi. 1882. Thysanoteuthis, Vigelius, Mitth. Zool. Stat. Naples, ii. 

 1881. 



Cartilage of Cephalopoda, Fiirbringer, M. J. iii. 1877. 



Homology of siphon and arms, Brooks, American Journal of Science and Art, 

 xx. 1880. 



Spirula, Owen, A. N. H. (5), iii. 1879; P. Z. S. 1880. 



Gigantic Cuttle-fish, &c., Verrill, U. S. Commission of Fish and Fisheries, 

 Report for 1879, Part vii. Washington, 1882. 



Hh 



