188 INVERTEBRATE ANIMALS. 



The body in the Cephalopoda is symmetrical, and is en 

 closed in an integument which may be regarded as a modificaN 

 tion of the mantle of the other Mottusca. Ordinarily there it 

 a tolerably distinct division of the body into an anterior por- 

 tion, carrying the head, and a posterior portion, in which 

 the internal organs are enclosed. The head (Fig. 89) 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 arms, which are generally provided with rows of suckers. 

 Each sucker consists of a cup-shaped cavity, the muscular 

 fibres of which converge to the centre, where there is a 

 little muscular eminence. When the sucker is applied to any 

 surface, the contraction of the radiating muscular fibres de- 

 presses the central eminence so as to produce a vacuum below 

 it, and in this way each sucker acts most efficiently as an ad- 

 hesive organ. The whole of this complex mechanism of suckers 

 is completely under the control of the animal, and the ir- 

 ritability 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. 89), there are ten processes round the mouth, 

 of which eight are like each other, and constitute the true 

 arms, while two called tentacles are much longer than the 

 others, and bear suckers only toward their extremities, which 

 are enlarged and club-shaped. The Paper Nautilus (Fig. 90) 

 has two of the arms webbed at their extremities and secreting 

 a shell ; and the Pearly Nautilus, alone of all living Cephalo- 

 poda, 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 working vertically, very 

 like the beak of a bird, together with an " odontophore " or 

 " tongue," the hinder part of which is furnished with recurved 

 spines. This cavity leads by a gullet, furnished with salivary 

 glands, into a stomach, from which an intestine is continued 

 to terminate by a distinct anus, which opens on the ventral 

 surface at the base of the so-called " funnel." The funnel is a 

 muscular tube placed on the under surface of the head, and 

 communicating on the one hand with the external medium, 

 and on the other with the cavity of the mantle. In the Naw- 

 tilus alone it is simply formed of two muscular lobes, which 

 are in apposition, but are not united together so as to form a 

 tube. In many cases there is also a special gland, known as 



