Introduction to A nimal Morphology. 3 1 3 



CHAPTER XXXVIII. 



CLASS 3. — CEPHALOPODA. 



Marine, carnivorous, dioecious, symmetrical molluscs, 

 the highest of the sub-kingdom; with partially cleft 

 ova ; a distinct head surrounded by the modified foot ; 

 respiration branchial ; sense-organs well developed ; 

 the bodies are antero-posteriorly shortened and verti- 

 cally elongated ; they creep with the head downwards, 

 and swim laterally with their upper side forwards. 



The integument is smooth, rarely papillose, covered 

 by a porous cuticle of united cylinder (Nautilus) or 

 pavement cells, on a basis of fibrillar tissue, beneath 

 which are one or two layers* of nucleated pigm.ent 

 cells with contractile processes (chromatophores). 

 The pigment is rarely in the surface epithelium. t 

 Under these is often a layer of lamellar, highly re- 

 fracting corpuscles [JlitterchenX) producing by inter- 

 ference a play of colours. 



Beneath these layers, loose connective tissue covers 

 a muscular and connective substratum, containing 

 usually a network of capillary blood-vessels. The in- 

 tegument of the sides of the body is differentiated into 

 a mantle which incloses a cavity whose opening is 

 directed downwards (backwards in progression), and 

 which lies on the posterior (or what is generally con- 



* Wlien of two layers they are of different colours. 



t As in the tentacles and about the eyes of Nautilus ; some of those 

 cells are ciliated. 



X The chamaeleon-like change of colour, so striking in Cephalopods, is 

 ■due both to the changes in shape and size of the chromatophores and to 

 these jlitterchen. 



