. The biology of the amphibia. Amphibians. 324 THE BIOLOGY OF THE AMPHIBIA portions exposed to the air (Hopkins, 1926). In thoroughly aquatic forms the mucus does not form a layer and the hairs stand out in the water in the nasal passage. Thus, in neither case does the mucus form a medium in which odorous substances are dissolved before they stimulate the hairs. The olfactory hairs of Amphibia are functional both in an air and in a water medium, as has been well shown in the case of the newt (Matthes, 1926). The olfactory organ, however, reaches its highest state of development in terrestrial
. The biology of the amphibia. Amphibians. 324 THE BIOLOGY OF THE AMPHIBIA portions exposed to the air (Hopkins, 1926). In thoroughly aquatic forms the mucus does not form a layer and the hairs stand out in the water in the nasal passage. Thus, in neither case does the mucus form a medium in which odorous substances are dissolved before they stimulate the hairs. The olfactory hairs of Amphibia are functional both in an air and in a water medium, as has been well shown in the case of the newt (Matthes, 1926). The olfactory organ, however, reaches its highest state of development in terrestrial forms. In the larvae of frogs and salamanders the olfactory stream passes. H. Fig. 116.—Diagram of the olfactory epithelium of a frog. The long hairs reach the surface of the mucus and are non-moving. The shorter ones fail to reach this surface and exhibit ciliary activity. , olfactory epithelium; , long, non-moving, olfactory hairs; , surface of mucous layer; , short, moving, olfactory hairs. (After Hopkins.) freely inward from the nasal cavity to the mouth. Its return to the nasal passage is prevented in urodele larvae by a simple flap of mucosa acting as a valve, while in tadpoles a double fold or fringe has a more complex form but similar function. During metamorphosis the choanal valves are lost and a new mechanism for closing the nasal passage appears at its other end. As shown by Bruner (1901, 1914), a constrictor and two dilators of the external nares develop at this time or shortly before the choanal valves are lost. In metamorphosed Amphibia the olfactory stream under muscular control passes freely in and out through the nasal cavity. The inspired stream tends to move through. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Noble, Gladwyn Kingsley, 1894-1940. New York : McG
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Keywords: ., bookcentury1900, bookpublishernewyorkmcgr, booksubjectamphibians
