. Elementary text-book of zoology. Zoology. CEPHALOPODA. 59 Mil opening of the mantle being firmly closed by the sucker-like arrange- ment at the base of the funnel; the animal, in consequence of the reaction, is thus projected backwards. Many Cephalopoda are naked (Octopoda), others (Decapoda) posse-- an internal rudimentary shell, a few (Argoncmta, Nautilus) are pro- vided with an external spirally-coiled shell. The internal shell rudiment of the Decapoda lies in a pocket in the dorsal mantle, and is usually a flat, lancet-shaped spongy calcareous plate (os sepi(e). The external shell is onl
. Elementary text-book of zoology. Zoology. CEPHALOPODA. 59 Mil opening of the mantle being firmly closed by the sucker-like arrange- ment at the base of the funnel; the animal, in consequence of the reaction, is thus projected backwards. Many Cephalopoda are naked (Octopoda), others (Decapoda) posse-- an internal rudimentary shell, a few (Argoncmta, Nautilus) are pro- vided with an external spirally-coiled shell. The internal shell rudiment of the Decapoda lies in a pocket in the dorsal mantle, and is usually a flat, lancet-shaped spongy calcareous plate (os sepi(e). The external shell is only exceptionally thin and simple (Anjonautci); usually it is spirally- twisted and divided by cross partitions into a number of successive chambers. The animal lives in the anterior chamber, which is the last formed and largest. The other chambers, which diminish continuously in size backwards, are filled with air; they L4~ remain, however, connected with the large anterior chamber by a central tube (.yip/ton), which perforates the partitions and contains a prolongation of the animal's body. The dermis of the Cephalopoda contains- the remarkable chromato- phores, which cause the well-known play of colours. These consist of cells filled with pigment; to their walls, which are formed of a cellular mem- brane, numerous radiating muscular FIG. 532.—Digestive apparatus of Sepia /.,Ti \\T V.*es,-~r,-t-s*lr,\ T lil-i • Af'Ci 17 i',- fibres are attached. When the latter contract the cells are pulled out into a star shape; in the processes so formed the pigment is distributed. When the contraction ceases, the cell returns, in virtue of the elasticity of its walls, to its original spherical form and the pigment is again concentrated in a small space; thus the animal changes its colour. There are usually two kinds of chromatophores, as far as colour is concerned, placed above and near one another. They are connected with a special centre. (after W. Keferstein). L, lip ; Mxi, «, low
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
