Receiving molecules chemosensory organs

Apart from taste, vertebrates have five different chemoreceptor systems for airborne chemosignals the main olfactory system, the vomeronasal organ (VNO), the trigeminal nerve, the septal organ of Masera, and the nervus termi-nalis. They each will be discussed in turn. All five are fully functional in most mammals (Fig. 5.1). 

This chapter will only deal with a few facts pertinent to the ecological operations of animals. Excellent reviews and monographs deal with the olfactory system. 

Elasmobranchs have their paired olfactory organs on the ventral side near the mouth. As the fish takes the respiratory water current into the mouth, water passes through the olfactory sacs. Thus, elasmobranches use the respiratory water current for supplying the olfactory organ with waterborne stimuli. 

By contrast, bony fish have their olfactory organs on the dorsal side of the snout at some distance from the mouth. The olfactory system in fish involves the first (olfactory) cranial nerve, while the ninth (glossopharyngeal) and other nerves serve the sense of taste. 

FIGURE 5.2 The olfactory organ in fish, (a) The nostril positions in sculpin (Cottidae) b) nostril position in spiny eel (Mastacembelidae) (c) a skin flap separates in- and outflow, an arrangement typical for bony fish (here Catastomidae) (d) the olfactory lamellae are located in the floor of the olfactory capsule (here minnow, Phoxinus). (From C. E. Bond Biology of Fishes.) 

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