. Text book of zoology. Zoology. Glass 2. Pisces. 369 TeleosteanSj Selacliians); in others, a transverse membranous bridge, varying in width, divides the opening into two, anterior and posterior nares, of which the anterior may occasionally be drawn out into a narrow tube; in many Selachians, this bridge is only represented by a flap, arising from one side, and overlying the aperture without being attached to the other. In tlie Dipnoi, tte nasal openings are peculiar, in that both lie within the edge of the upper lip. In the Oyolostomes, the two olfactory pits are united to form a deep unpahed
. Text book of zoology. Zoology. Glass 2. Pisces. 369 TeleosteanSj Selacliians); in others, a transverse membranous bridge, varying in width, divides the opening into two, anterior and posterior nares, of which the anterior may occasionally be drawn out into a narrow tube; in many Selachians, this bridge is only represented by a flap, arising from one side, and overlying the aperture without being attached to the other. In tlie Dipnoi, tte nasal openings are peculiar, in that both lie within the edge of the upper lip. In the Oyolostomes, the two olfactory pits are united to form a deep unpahed tubular sac, the floor of which Ues closely upon the roof of the mouth; in Myxine, it perforates the roof of the mouth, and consists of a tube open at both ends, connecting the oral cavity with the exterior. Taste buds, as already mentioned (p. 21), are present in many Fish (Teleostei), not only in the mouth, but scattered over the surface of the body. Groups of peculiar sense-organs occur in connection with the skin; they consist of modified epidermal cells, some of which bear sensory hairs; and are thus not unlike taste-buds, from which, how- ever, they differ in form. These sensory papillee are supplied with nerves, and may lie free upon the surface of the body {, in most Teleostei), in which case they often bear a cylindrical tube, a cuticular structure, which surrounds and protects the hairs (Fig. 305 r). In other cases, those portions of the skin to which they belong, have sunk in to form small sacs, opening to the exterior (Ganoids); or the sacs have become long tubes filled with mucus, running below the skin, provided at one end with an expansion in which the sensory cells lie, whilst at the other, they open to the surface (on the head in Selachians). Further, similar groups of cells are present in the lateral line which occurs in most Fish. This is a narrow tube (an invagination of the skiti), lying close below the surface, and extending along each side of the bod
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1896
