CEPHALOPODA. 



209 



integument which may be regarded aa a modification of the mantle 

 of the other Molluscu. Ordinarily there is a tolerably distinct divi- 

 sion of the body into an interior portion, carrying the head, and a 

 posterior portion, in which the anternal organs are enclosed. The head 

 (fig. 148) is very distinct, bearing a pair of large globular eyes, and 

 having the mouth in its centre. The mouth is surrounded by a 

 circle of eight, ten, or more, long muscular processes, or arm.s, which 

 are generally provided with 

 rows of suckers. Each sucker 

 consists of a cup-shaped cav- 

 ity, the muscular fibres of 

 which converge to the centre, 

 where there is a little mus- 

 cular eminence or papilla. 

 When the sucker is applied 

 to any surface, the contrac- 

 tion of the radiating muscular 

 fibres depresses the papilla so 

 as to produce a vacuum be- 

 low it, and in this way each 

 sucker acts most efficiently as 

 an adhesive organ. The whole 

 of this complex mechanism of 

 suckers is completely under 

 the control of the animal, and 

 the irritabilitjf of the suckers 

 is retained even for days after 

 death. In most of the Cuttle- 

 fishes (Octopoda) there are 

 only eight arms, and these are 

 nearly similar to one another. 

 In others, however (fig. 148), 

 there are ten processes round 

 the mouth, of which eight are 

 like each other, and constitute 

 the true arms, whilst two — 



called tentacles — are much longer than the others, and bear suckers 

 only towards their extremities, which are enlarged and club-shaped. 

 The Paper Nautilus (fig. 151) has two of the arms webbed at their 

 extremities and secreting a shell ; and the Pearly Nautilus, alone 

 of all living Cephalopoda, has numerous arms, more than ten in 

 number, and destitute of suckers. 



The mouth leads into a cavity containing two powerful horny or 

 partially calcareous jaws or mandibles, working vertically, very like 



Fig. 149. — Diagram of a Cuttle-fish (altered 

 from Huxley) ; m Mandibles ; n Cerebral 

 ganj^lia ; I Liver ; p Intestine ; o Ovary ; g 

 Gill ; i Ink-bag ; /Funnel : s Internal skele- 

 ton, or "cuttle-bone." 



