128 



CLASS MOLLUSC A. 



SUB-CLASS CEPHALOPODA. 



interesting than the poetical description given of this beautiful animal seute.l 

 in its pearly little vessel, its sails spread, and the remaining six tentacula 

 serving for its oars. On the slightest appearance of danger, it withdraws 

 itself into its shell, and is instantly submerged. 



Illustrations : Argonauta varicosta, A. Argo. Exemplified in the Paper 

 Nautilus and Ocythoe Cranchii. 



The Paper Nautilus, or Paper wZor( Plate 1, fig. 3-8), lias from a remote 

 l>eriod from before the days of Aristotle to the present time been an 

 object of much interest to zoologists. It has been regarded as the first 

 instructor of man (by its own example) in the art of navigation ; and many 

 romantic and fabulous stories of its wonderful sailor-like skill have come 

 down to us from ancient times. A difference of opinion respecting the 

 shell occupied by this cephalopod, lias also added to its interest as an object 

 of zoological inquiry some naturalists maintaining (among whom is Dr. 

 Owen) that the animal is itself the original fabricator of its shell, while 

 others (Dr. Leach, De Blainville, &c.) have asserted an opposite opinion, 

 viz., that the cephalopod is either a mere ]>arasite as the Cancer Bar- 

 nardus, and other parasitical Crabs or that it is nothing short of being a 

 piratical intruder, who, having dispossessed the projier owner, became the 

 lawless occupant of his dwelling. The former opinion is, however, now 

 generally admitted as correct ; for the experiments of Madame Power, and 

 the anatomical researches of Dr. Owen, have placed the matter almost 

 beyond dispute. 



The characteristics of the Paper Nautilus are body oblong and rounded ; 

 mantle adhering to the head posteriorly ; dorsal or first pair of arms 



Paper Nautilus. 



membranous and dilatable at the extremities ; funnel destitute of a valve, 

 but articulated at its base to the inner sides of the mantle by two ball-and- 

 socket joints ; heart branchial, with fleshy appendages ; no horny or testa- 

 ceous internal rudiments; body contained in an external, monothalmous, 

 and symmetrical shell, but not attached to it ; the animal deposits its eggs 

 in the spiral cavity of the shell. The molluscous animal inhabiting the 

 beautiful and fragile bark already described is named Ocythoe, one species 

 of which is shown on Plate 1 (figs. 1, 2). 



The Ocythoe Cranchia is, according to Leach, of the family Decaccera, 

 having tentacular appendages, ten in number; it is found in Ouvn's 

 Teuthidoe. The animal is characterised by an elongated, sacciform body ; 

 natatory appendages, or fins, ten in number, circular and of small size, 

 pedunculated and nearly touching each other at their origin at the back : 

 dorsal piece altogether wanting (Plate 1, figs. 1,2). 



The Cephalopod is furnished with three stomachs an cesoplmgus, a 

 gizzard nearly as fleshy as that of birds, and a spiral and membranous cavity 

 in which the liver discharges its bile. The respiratory current passes through 

 a fleshy pipe or funnel situated in front of the neck and communicating 

 with the branchial. These organs are protected by the mantle under which 

 they are concealed. In the higher-organized Cephalopods three distant 

 hearts are found, while in those of the lowest organization only one heart is 

 discoverable. The eye, which is covered by a transparent portion of the 

 skin, is composed of numerous membranes ; the ear is a simple opening, in 

 which a membranous sac is suspended containing a limpid fluid, and a small 

 stony substance or otholithe. The skin of the naked species is changeable 

 like the skin of the Chameleon. Some of the Cephalopods are furnished 

 with a bag containing an inky secretion, which they carefully reserve till an 

 occasion arises necessary for its effusion, thus blackening the surrounding 

 water, under cover of which they generally effect their escape. 



Four of the principal genera are as follow : 



LoLIGO. Body long, with two angular fins on the hinder part of the 

 back, on each side of the tail ; the support 

 cartilaginous, pen-shaped. This genus 

 was separated from the Sepia, or Cuttle- 

 fish of Linnaeus, by Lamarck ; they are ' 

 usually called Sea-sleeves, and their bone 

 a Sea-pen. 



The type of the genus is L. Media, the 

 Sepia loligo of Linnjeus, common on the 

 English coast. 



One species, Loligopsis, is remarkable 

 for the extreme length and gracility of 

 its two arms. 



NAUTILUS. Shell discoid, spiral, mul- 

 tilocular, with simple sides, the latter 

 equal; whorls contiguous, the last em- 

 bracing and concealing the previously- 

 formed ones ; septa transverse. 



Type of the genus, 

 N. pompilius. This is an 

 extensive genus, consist- 

 ing of recent and extinct 

 species ; the former ma- 

 rine, and several of both 

 found on the coasts and 

 crags of Britain. 



OCTOPUS. Body 



fleshy, obtuse beneath, 

 and contained in a sac, 

 which has no wing-like 

 appendages, nor inter- 

 nal dorsal bone, or a 

 very minute one only ; 

 head distinct, furnished 

 with a terminal mouth, 

 armed with two horny 

 mandibles, and sur- 

 rounded with eight sim- 

 ple, elongated arms, fur- 

 nished with sessile suckers. 



Type of the genus, the Sepia octopus, of Sowerby, the O. vulgari* of 

 Fleming. Several species, three of which are found on the British c> 



a, portion of mantle ; 6, foot ; r, tentacula ; d, funnel : 

 e, eye ; /, siphon. 



Pearly Nautilus; shell laid op 



