Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0201clau Year: 1884 SENSE ORGANS. 121 The sense organs present the following arrangement. The anterior is the olfactory organ, which consists of a pit usually paired, excep- tionally unpaired (Cyclostornes); the nerves which pass to these pits arise from the fore-brain and are often swollen at their origin into special lobes (olfactory lobes). In aquatic animals which breathe by gills the nasal cavity consists with rare exceptions (Mi/.i-lne] of a blind sac. In all lung-breathing Vertebrates, on the contrar
Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0201clau Year: 1884 SENSE ORGANS. 121 The sense organs present the following arrangement. The anterior is the olfactory organ, which consists of a pit usually paired, excep- tionally unpaired (Cyclostornes); the nerves which pass to these pits arise from the fore-brain and are often swollen at their origin into special lobes (olfactory lobes). In aquatic animals which breathe by gills the nasal cavity consists with rare exceptions (Mi/.i-lne] of a blind sac. In all lung-breathing Vertebrates, on the contrary, it communicates with the cavity of the mouth by the nasal passages, and serves for the entrance and exit of the pulmonary air. Next come the eyes with the optic nerves which arise from the thalamencephalon and mid-brain. They are always paired (for the structure of the eye vide p. 73, vol. i.). In Am- phioxus alone they are represented by an un- paired pigment spot placed on the anterior end of the central nervous system. The auditory organ, the nerve of which belongs to the hind-brain (probably derivecl from the sensory root of a spinal-like cranial nerve), is entirely absent in AmphioXUS. In its simplest Fi& 578 _Dia?ram of the auditory labyrinth (after Waldeyer). I, of fish; II, of bird; ///, of mammal; U, utricle with the three semicircular canals ; S, saccule; US, alveus communis; C, cochlea; L, lagena; Cr, caualis reuniens ; R, aquteductus vesti- bull. form it is a membranous sac (membranous labyrinth) containing fluid and oto- liths. The posterior part of this sac is usually prolonged into three semi-circular canals, while the anterior part, which in many cases is separated as the saccule, gives off a prolongation which forms the cochlea (fig. 578, />', C.). The sense of taste is located in the palate and the root of the tongue. The organs of taste consist of peculiarly-modified groups of epithelial cells (taste buds), and are supplied by a spinal-like cerebral
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