^ 235. THE CErnALOPODA. 273 



covered by its anterior border. <^> The sea-water, which enters into the inte- 

 rior of the mantle, passes, with its various contents, into this funnel, and is 

 thence expelled through its anterior orifice. 



Many Cephalopoda have, on the dorsal wall of this organ directly behind 

 the anterior orifice, a tongue-shaped valve, which prevents the reflux of the 

 water.*-* 



With the Loligina, the sides of the trunk have variously-shaped cutaneous 

 lobes, which these animals use as fins.*^* The Octopoda, on the other hand, 

 swim by rowing with their arms, which are bound together at their base by 

 a kind of natatory membrane, whose extremities have, each, a broader or 

 narrower cutaneous dilatation.'"** 



§ 235. 



The mantle of many of the Cephalopoda secretes a shell, which may 

 be either external or internal. 



1. An external shell is found with Argonauta and the Nautilina. That 

 of the Paper-Nautilus is very thin and flexible, — and, in its composition, 

 the organic base predominates above the calcareous matter, which consists 

 of thickly-set, small, round masses. The substance of the shell, which, with 

 Argonauta, is nowhere attached to the animal it encloses, is secreted prin- 

 cipally by the two large cutaneous lobes of the two median dorsal arms, 

 which lie upon the external surface of the shell. On this account, the 

 structure of the two surfaces of these lobes is difi'erent ; — the external sur- 

 face is quite smooth and has many chromatic cells ; while the internal has 

 scarce any of these last, but is covered with numerous reticulated, project- 

 ing lines, which become the more prominent when the lobes are contracted, 

 and between which, cell-like depressions are formed.'^' 



With the Nautilina, the shell has a very complicated structure ; its walls 

 are composed of two distinct layers, clearly separate, the intexMial of which 

 has a beautiful mother-of-pearl aspect. The cavity of the shell is divided, 

 even to the last spiral turns, by numerous transverse septa, which are all 

 perforated. With Nautilus,^^^ a tube traverses the septa, while with 



1 With Nautilus, the funnel is coipposed of two In this same genus, as also with Argonauta, thir 



pretty larsje, cutaneous lobes, placed upon both sides two dorsal arms are terminated by a very larf;e 



of the throat, and reciprocally covering each other cutaneous lobe, and are used not only as locomo- 



on the ventral surface in a cornet-like manner ; tive organs, but also for keeping the shell in place 



see Owen, On the Nautilus, p. 10, PI. I. or Isis. p. by being applied on its external surface ; see Fe- 



10, or Ann. d. Sc. Nat. loc. cit. p. 93, PI. I. III. russac, loc. cit. Argonauta, PI. I. fig. 5, 6, PI. VI. 



and Valenciennen loc. cit. ]>. 269, PI. X. fig. 1. fig. 2, and in the Mim. de la Soc. d'Hist. Nat. de 



■2 This is so with Sepia, Sepiola, Loligo, Se- Paris, II. 1825, p. 160, PI. VI. fig. 2, or Isis, 1832, 



pioteuthis, Onychoteuthis, and Nautilus. For p. 460, Taf. V. fig. 2 ; Rang, Docum. pour servir 



this last, see Owen, loc. cit. PI. II. fig. 2, e., and i. I'Hist. nat. des Cephalopodes, in the Magaz. 



yalenciennes, loc. cit. PI. XI. fig. 4, ;.. I have de Zool. 1837, Livr. IV. p. 19, H. LXXXVI.- 



sought for it in vain with Argonauta, Eledone, LXXXVIII., or Ann. d. Sc. Nat. VII. 1837, p. 



and Tremoctopus. It is also wanting with Loli- 176 ; and Delle Ckiaje, Descriz. loc. cit. Tav. VII. 



gopsis and Cranchia ; with Octopus, there e.\ists fig. 1, 2. 



in its place, that is, on the ventral surface of the 1 It has been attested by several observers, that 



funnel, a transverse ridge. these two cutaneous lobes furnish the substance of 



S With Sepia, and Sepioteuthis, both sides of the shell, and that, also, with which the animal re- 



the body are bordered their entire length with a pairs accidental lesions ; see Rang, MagiU. de 



cutaneous lobe. With Loligo, and Onychoteuthis, Zool. loc. cit.; Jeanette Power, in the Atti dell' 



the two fins are triangular and inserted on the Acad, di Scienz. Nat. di Catania, XII. 183!). 



posterior extremity of the body ; they are round or Isis. 1845. p. f>06, or in IViegmann's Arch, 



and short with Sepiola, Loiigopsis, and Cranch- 1845, 1, p. 369 ; and, Further experiments and ol>- 



ia ; in the first of these genera, they are situated serv. on the Argonauta Argo, in the Keports of 



on the middle of the sides of the body, and in the the Brit. Assoc. 1844, Notices and Cimnnunic. j). 



last two, upon its extremity. 74. For the non-parasitism of Uie animal, sec, 



■4 These interbranchial natatory membranes ex- moreover, Fan Beneden, loc. cit. p. 4, and t'erus- 



ist with Octopus, Eledone, sind Tremoctopus ; .?ac, loc. cit. p. 114. 



they are jiarticularly developed in this last geuus, - De Blainville, in the Nouv. Ann. du Musenni 



between the two pairs of dorsal arms. d'Hist. Nat. III. 1834, p. 3, PL I. II. 



