THE CEPHALOPODA. 445 



terior, or anal, face of the sac, the mantle incloses a large 

 pallial cavity, in which the branchiae are protected. On the 

 anterior aspect of the sac, on the contrary, the mantle may 

 have no free edge, or, at most, forms a comparatively small 

 flap. 1 



The integument is provided with chromatophores, which 

 are sacs with elastic walls, full of pigment, and provided with 

 radiating muscles, by which they may be drawn out to a size 

 many times greater than that which they possess in their 

 contracted state. In their dilated condition, the color proper 

 to the contained pigment becomes plainly visible, while in 

 their contracted state they appear as mere dark specks. It 

 is to the successive expansion and contraction of these chro- 

 matophores that the Cephalopoda owe the peculiar play 

 of "shot" colors, which pass like blushes over their sur- 

 face in the living state. These blushes of color are especial- 

 ly well displayed by young Cephalopods just freed from the 



egg- 



But that which particularly distinguishes the Cephalo- 

 pod is the form and disposition of the foot. The margins 

 of this organ are, in fact, produced into eight or more pro- 

 cesses, termed arms, or brachia y and its antero-lateral por- 

 tions have grown over and united in front of the mouth, 

 which thus comes, apparently, to be placed in the centre of 

 the pedal disk. Moreover, two muscular lobes which cor- 

 respond with the epipodia of the Pteropods and Branchio- 

 gasteropods, developed from the sides of the foot, unite pos- 

 teriorly, and, folding over, give rise to a more or less com- 

 pletely tubular organ, the funnel, or infundibulum. The 

 open end of the funnel projects between the posterior face 

 of the body and the pallial wall of the branchial cavity, and 

 serves to conduct the water, when it is driven out of the 

 latter by the contraction of the mantle in ordinary expira- 

 tion ; and when the animal swims, the stream forcibly driven 

 out in this way causes it to dart swiftly backward. 



The aperture of the mouth (Fig. 125, a) is provided with 

 a hard, chitinous beak, like that of a parrot, the two divis- 

 ions of which are anterior and posterior. Of these, the 

 anterior is always the shorter, and is overlapped by the 

 other. 



1 Cephalopods are usually described as if the oral end of the body were the 

 upper end, and the face on which the pallial chamber is placed 'ventral — a 

 method which seriously interferes with the comprehension of their relations 

 with other Mollusks. 



