. A manual of zoology. Zoology. GENERAL ORGANOLOGY 117 thousands, may remain separate. In a definite region of the epithelial wall the sensory cells are developed into the crista aciistica or the auditory ridge; they are in connection with the auditory nerve and bear the auditory hairs projecting into the endolymph. The otoliths are usually free in the centre of the vesicle, or are often held in place by bundles of cilia which project from the non-sensitive epithelial cells. Every auditory vesicle develops from a pitlike invagination of the skin, and consequently is for a time an auditory pit.
. A manual of zoology. Zoology. GENERAL ORGANOLOGY 117 thousands, may remain separate. In a definite region of the epithelial wall the sensory cells are developed into the crista aciistica or the auditory ridge; they are in connection with the auditory nerve and bear the auditory hairs projecting into the endolymph. The otoliths are usually free in the centre of the vesicle, or are often held in place by bundles of cilia which project from the non-sensitive epithelial cells. Every auditory vesicle develops from a pitlike invagination of the skin, and consequently is for a time an auditory pit. Therefore it is not surprising that in many animals the organ has stopped at the lower stage of development; for example, the crayfish has an open auditory pit (fig. 378). On the other hand, the auditory vesicle may develop a com- plicated system of cavities as in mammals (fig. 83), where it is divided by a constriction into the sacadus and the utriculiis. The sacculus is pro- O. '—U Fig. 83.—Diagram of the human labyrinth. U, utriculus with the semicircular canals; 5, sacculus connected with the cochlea (C) by the canalis reuniens; R, recessus labyrinthi; V, blind sac of the cochlea; K, apex of the cochlea. vided with a spirally-wound blind sac, the cochlea, the utriculus with the three semicircular canals, the whole being called the labyrinth. In addi- tion there is formed in most vertebrates, a sound-conducting apparatus, so that the auditory organ acquires a very complicated structure. Other Forms of Auditory Organs.—Since there are animals without auditory vesicles which hear well, like the spiders and insects, we must assume that there are auditory organs of another type. Still we have no certain knowledge of these except in the case of the tympanal auditory organs of the grasshoppers (see p. 4ro). Function of the Semicircular Canals.—Experiments upon repre- sentatives of the different classes of vertebrates have led to the conclusion that the three semicircular
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
