. Text book of zoology. Zoology. 320 Mollusca. and is further provided with a lens; the inner half of which is secreted by the epithelium of the optic vesicle; the outer half by the epidermis. Moreover, at the periphery of the eye, a large fold like an eyelid is present, forming a cavity round the eye; in some Decapoda {(Ugopsidce, Fig. 265 B) this cavity is widely open; in the rest {Myopsidce) and in the Octopoda (Fig. 265 C) the fold extends completely round the eye, and the aperture leading into the cavity is very small; where the fold lies above the lens it is transparent, and is termed th
. Text book of zoology. Zoology. 320 Mollusca. and is further provided with a lens; the inner half of which is secreted by the epithelium of the optic vesicle; the outer half by the epidermis. Moreover, at the periphery of the eye, a large fold like an eyelid is present, forming a cavity round the eye; in some Decapoda {(Ugopsidce, Fig. 265 B) this cavity is widely open; in the rest {Myopsidce) and in the Octopoda (Fig. 265 C) the fold extends completely round the eye, and the aperture leading into the cavity is very small; where the fold lies above the lens it is transparent, and is termed the cornea. In the cavity thus formed there is a second small pigmented fold, which displays a certain resem- blance to the iris of the Vertebrata, and is also designated by that name. A depression of the skin situated laterally on the head behind the eyes and supplied by a nerve from the brain, is regarded as an olfactory organ. The mouth is surrounded by a projecting fold of skin, the lip, within which are two powerful horny jaws, an upper and a lower; the former bites within the edge of the latter, and the two together are very similar to a parrot's beak inverted. In the mouth, which is furnished with muscular walls, there is a radula like that of the Gastropoda. The anus lies far forward on the ventral side of the body in the mantle-chamber, in the median line. A stomach, a large liver, and usually salivary glands are present. The heart consists of a ventricle and as many auricles as there are gills, that Fig. 266. Diagram of the heart, etc. of a Cephalopod. h ventricle, / auricle, u, « arteries, vh branchial heart, of vein to the giU, vf vein from the gill, g gill.—Orig. four in Nautilus, two in other Cephalopods. In the Dibranchiata the large veins which carry the blood to the gills are known as branchial hearts; they are enlarged at the entrance of the gills and contractile. The kidneys, two pairs in Nautilus, one pair in the Dibranchiata, are saccular organs openi
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1896
