CEPHALOPODA. 417 



Class V. CEPHALOPODA.* 



With well-marked head, a circle of processes bearing suckers or 

 tentacles round fhe mouth, and a funnel composed of two separate 

 or fused halves. Tlie genital coelom is continuous with the peri- 

 cardia!. Dioecious. 



The Cephalopoda are symmetrical animals with a much-shortened 

 antero-posterior axis, and with a strongly -developed visceral sac, 

 which has undergone neither torsion nor asymmetrical development, 

 and which is, except in Naiitilus, unprotected by an external shell. 

 The mantle-fold is circular and the mantle- cavity is especially 

 developed on the posterior side of the visceral sac ; in it are placed 

 the ctenidia, either two (Dibranchiata) or four (Tetrabranchiata), 

 and into it open the median anus, the ink-sac, the paired kidneys, 

 and the genital duct. There are always processes round the 

 mouth, which are either lobe-like and carry tentacles as in the 

 Tetrabranchiates, or are arm -like and carry suckers as in the 

 Dibranchiates. They are active, voracious animals, with a complex 

 organization, highly developed sense-organs, and often possessed of 

 considerable intelligence. The Cephalopoda are marine animals, 

 some frequenting the coast, others the high seas, and some the 

 floor of the ocean to a depth of nearly 2000 fathoms. About 400 

 species are known. They feed on the flesh of animals, especially 

 Crustacea, and some of them attain a great size.f The flesh is 

 eaten, and the colouring matter of the ink-sac (sepia) and the dorsal 

 shell (os sepiae or cuttle-bone) are used by man. The remains of 

 Cephalopods occur in all formations from the Cambrian, and con- 

 stitute important characteristic fossils (Belemnites, Ammonites). 



Ferussac et d'Orbigny, " Histoirc natureUe generate et particuliere des 

 Cephalopodes acetabulifircs vivants et fossiles," Paris, 1835-45. J. B. Verany, 

 " Mollusques meditcrranes observes, etc., d'apres Ic vivant," l e Partie, Genes, 

 1847-51. H. Miiller, " Ueber das Mannchen von Argonauta argo u. die Hec- 

 tocotylen," Z. f. w. Z., 1855. Jap. Steenstrup, " Hectocotyhis dannelsen hos 

 Octopodsl., etc., "-.ST. Danks. Vidensk. Selskabs Skriftcr, 1856 ; translated in 

 Archiv. f. Nalurgcsch., 1856. C. Grobben, " Morphologische Studien lib. den 

 Harn-u. Geschlechtsapparat, etc., der Cephalopoden," Arb. a. d. Zool. lust. 

 Wien, 5, 1884. W. E. Hoyle, "Report on the Cephalopoda," Challenger 

 Reports, vol. 16, 1886. J. Brock, " Zur Anat. u. Syst. d. Cephalopoden," 

 Z. f. w. Z., 36, 1882. P. Pelseneer, " Sur la value morphologique des bras et la 

 composition du syst. nerv. cent. d. Cephalopodes," Arch. Biol. 8, 1888. 

 Milne-Edwards et Valenciennes, " Obs. sur la circulation chez les Mollusques," 

 Mem. Acad. Sci. Paris, 20, 1840. Vigelius, " Ueb. d. excretionssystem der 

 Cephalopoden," Nicderl. Arch. f. Zool., 5, 1880. Milne -Edwards, "Sur les 

 spermatophores des Cephalopodes," Ann. Sci. Nat. Zool. (2), 18, 1842. 



f Specimens of Architeuthis have been taken measuring from apex of visceral 

 sac to end of extended arms more than 50 feet, and with eyes 15 inches 

 across. 



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