. The biology of the frog. Frogs. 26 THE BIOLOGY OF THE FROG CHAP. which the tongue is covered enables it to adhere to the objects it strikes against, so that they may be conveyed to the mouth. The frog has an instinct to snap at small moving objects that come sufficiently near. This action is determined more by the motion and size of the objects than their form. Un- less a thing is moving, the frog pays little attention to it. Frogs may often be caught by dangling small bits of red yarn before them on a hook. When the yarn is seized, the animal may be jerked out of the water. According to Kna
. The biology of the frog. Frogs. 26 THE BIOLOGY OF THE FROG CHAP. which the tongue is covered enables it to adhere to the objects it strikes against, so that they may be conveyed to the mouth. The frog has an instinct to snap at small moving objects that come sufficiently near. This action is determined more by the motion and size of the objects than their form. Un- less a thing is moving, the frog pays little attention to it. Frogs may often be caught by dangling small bits of red yarn before them on a hook. When the yarn is seized, the animal may be jerked out of the water. According to Knauer, frogs and toads have the power of ejecting indigest- ible bodies from the stomach by way of the mouth. Bits of grass or moss accidentally swallowed with the food are gotten rid of in this way. Protrusion of the Tongue. - - The frog is able to throw out its tongue with remarkable rapidity, but the method by which this feat is ac- complished was, until recently, but inade- quately understood. Hartog1 and Gaupp 2 have found that the protrusion is brought about by the pressure of the lymph in the large sublingual lymph sac. This may be readily shown if we cut off the upper jaw of the frog and inject air or liquid through the mylohyoid muscle, which extends beneath the tongue. The lymph spaces become filled, and this causes the tongue 1 Hartog, Ann. Nat. Hist., May, (7), 7, 1901, 2 Gaupp, Anat. 19, FlG. 6. — Figure showing the tongue of the frog in three different positions. (After Wiedersheim.). 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 Holmes, Samuel J. (Samuel Jackson), 1868-. New York, London, Macmillan
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