276 THE CEPHALOPODA. § 238. 



posed others which are longitudinal, and, lastly, of a layer of circular fibres 

 directly beneath the skin.'" 



Over the entire length of the internal surface of these arms, are suckers, 

 arranged in a single, double, or multiple row.'-* But with the Loligina, 

 these suckers occur in groups of variable e.\tent only at the extrem- 

 ity of the ninth and tenth arras [tentacular arms). These suckers are 

 moved by muscular fasciculi which pass from the arms and are spread upon 

 the former in a ray-like manner, and which form, moreover, with the Loli- 

 gina, a peduncle. 



With Tremoctopus, iho suckers are cylindrical and very simple, while with 

 the other Octopoda, their opening is closed by a membrane perforated cen- 

 trally by an orifice which can be closed by a papilla that projects from the 

 base of the sucker.''^* These organs are applied to objects at the moment 

 when the papilla is withdrawn and removed to the base of the sucker. 

 With the Loligina, the lateral walls of the suckers are vei-y thin, extens- 

 ible, and have upon their borders a horny and denticulated ring ; in this 

 ring the fleshy base of the sucker adjusts itself in an urceolate form, and 

 upon withdrawal, produces a vacuum. With Loligopsis, and OiiychoteutJiis, 

 many of the suckers on the two tentacular arms are imperfect, but, on the 

 other hand, some of the teeth of their horny border are disproportionably 

 developed, or the whole is changed into a strong claw.'"" 



The arm-like processes about the mouth of Nautilus difier very much 

 f:-om the preceding. ''> They have no trace of suctorial organs, and are 

 composed of thirty-eight prismatic filaments, which are a little flattened and 

 transversely curled. 



Each of these filaments is surrounded, at its base, by a contractile sheath 

 into which it can be wholly withdrawn."^* The whole fasciculus is, moreover, 

 enveloj)ed in a common sheath, which, upon the back, is flattened so as to 

 resemble the foot of the Gasteropoda, and like it, probably, may serve for 

 creeping.'''* 



The portion of the skin, which extends as a kind of Natatory membrane 

 between the arms of many Cephalopoda, contains a very loose net-work of 

 longitudinal and transverse muscular fibres.'*'* 



The fins of the Loligina, have, on the contrary, large muscles composed' 

 of parallel, contiguous fasciculi which arise from the cartilages of these 

 organs, 



1 This axis is usually of a prismatic form ; con- 5 Otoen, and T'alenciennes, loc. cit. 

 sequently if an arm is cut transversely the section •< The internal structure of these filaments atrrees 

 presents a quiulrilateral or rhomboidal spot in its pretty closely with that of the arms of other ("e- 

 centre ; see i'auig'ni/, in the Descript. de I'Egypte, phalopoda. Oaen, Ou Cephalopods with chaml)er- 

 Hist. Nat. PI. I. fig. I. w.; Owen, in the Cyclop, ed shells, loc. cit. p. 8, fig. 13], Cycloj). loc. cit. p. 

 1. p. 528, fig. 214, c, and Ferussac, loc. cit. Octo- 526, fig. 213, and Arnials of Nat. Hist. XII. p. 

 pus, PI. II. fig. 3, and PI. XV. fig. 11, b. Asim- 305. 



ilar section of the body of an Hectocotylus pre 7 Owen, and Valenciennes, loc. cit. 



sonts a like aspect. 8 The large cataneous lobes of the median dorsal 



2 The suckers form a single row with E/cdoie ; arms of Treinoctojius and Ars:onauta, have a 

 a double one with the other Octopoda, and with similar structui-e. In this last genus, they are not 

 most of the Loligina ; but the rows are multiple used as oars, nor as sails, bvit are thrown back 

 with Sepia. upon the shell to keep it in place (§ 235, note 4) ; 



"> Although the double row of suckers on the they move in the water, moreover, like the other 



body of Hectocoti/lus does not diminish towards Cephalopoda, by the contractions of the mantle and 



the anterior extremity, yet, in other respects, it so the funnel (^linn;!, Magaz. d. Zool. 1S37, p. 22. I'l. 



closely resembles the suckers of Ars^niiauta and LXX.XVII.). It is therefore astonishing thai Jea- 



Trtmoctopus, that it may well be asked why this nette Power (^IViegmann''s Arch. 1845, I. i). 373) 



single fact was not sufficient to discover to the old- should have revived the old fable that these ani- 



9r observers the real nature of this pretended par- mals raise these two large arms above the surface 



asite. of the sea to be used as sails. 



* Firussac, loc. cit. Loligop.iis, PI. IV. and 

 Onychoieuthis, PI. VI. VIU. &c. 



