. The biology of the amphibia. Amphibians. 318 THE BIOLOGY OF THE AMPHIBIA chemical sense. The photoreceptors are the light receptors of eye and skin. The thermoreceptors are those especially sensitive to slight changes of temperature and embrace the temperature organs of the skin. In addition, there are pain receptors in both the skin and some internal organs which cannot be classified under any of these heads. For convenience of description the sense organs may be grouped ac- cording to their topographic positions. Lateral-line Organs.—The most conspicuous sense organs of the skin are the la
. The biology of the amphibia. Amphibians. 318 THE BIOLOGY OF THE AMPHIBIA chemical sense. The photoreceptors are the light receptors of eye and skin. The thermoreceptors are those especially sensitive to slight changes of temperature and embrace the temperature organs of the skin. In addition, there are pain receptors in both the skin and some internal organs which cannot be classified under any of these heads. For convenience of description the sense organs may be grouped ac- cording to their topographic positions. Lateral-line Organs.—The most conspicuous sense organs of the skin are the lateral-line organs. These are little clusters of sense cells usually forming shallow de- pressions in the surface and ar- ranged generally in definite rows on head and body. The lateral- line organs represent an inheri- tance from the fishes in which the same rows may be readily identi- fied. As in fishes these sense cells function in responding to vibra- tions of low frequency (Dye, 1921) in an aquatic medium. Lateral- line organs are present in all thoroughly aquatic urodeles and their larvae. They are present in showing nerve terminations about gome mountain-brook Species Such the sense cells. {After Chezar.) as the larger forms of Desmogna- thus, but are inconspicuous or lacking in the more terrestrial forms of the same genus. They are lacking in terrestrial plethodontids. Although present in larvae of all Ambys- toma, they show various stages of degeneration in the adults. Among the Salientia lateral-line organs are present in the aquatic larvae but usually are absent in the adults. They are found in the adults of the Pipidae (Escher, 1925) and of such very aquatic types as Bombina and Ceratophrys laevis. The lateral-line organs of Amphibia are less specialized than those of most fish in that they usually lie entirely within the epi- dermis. In Stereochilus they have sunk partly into the corium and. Fig. lateral 113.—Vertical section of a line organ of Siren lacertina.
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