. The biology of the amphibia. Amphibians. THE DIGESTIVE SYSTEM 209 in length. Great length without great bulk is secured by the narrowing of the tube and its twisting into a compact spiral. Most frog tadpoles feed largely on water plants and like other vegetarians require a maximum amount of absorbing surface. The winding of the intestine is not in one plane but extends ventrally as the spiral becomes narrower. There are usually two and a half to three loops, but as each loop is double, the winding seems more extensive. A few tadpoles living in the confined space between the leaves of bromeli
. The biology of the amphibia. Amphibians. THE DIGESTIVE SYSTEM 209 in length. Great length without great bulk is secured by the narrowing of the tube and its twisting into a compact spiral. Most frog tadpoles feed largely on water plants and like other vegetarians require a maximum amount of absorbing surface. The winding of the intestine is not in one plane but extends ventrally as the spiral becomes narrower. There are usually two and a half to three loops, but as each loop is double, the winding seems more extensive. A few tadpoles living in the confined space between the leaves of bromeliads or banana plants feed to a considerable extent on frog eggs. Their intestines do not have the characteristic watch-spring form of most tadpoles but are short and resemble the intestines of the adult frog in lacking a spiral. The more carnivorous tadpoles, such as those of Cera- tophrys dorsata, have a shorter digestive tract than herbivorous forms. It is probable that many of these differences in length and form of the intestines of tadpoles is due to the character of the food during each ontogeny (Fig. 79). In view of the experiments of Fig. 79.—Effect of food on the intestine of tadpoles. A. Intestine of a tadpole reared on a plant diet. B. Intestine of another reared on an animal diet. {After Babak.) Yung (1904, 1905), the mechanical effect of bulky food would seem to be greater than the chemical effect of plant tissues on the digestive tract of the tadpole. The experiments of Babak (1905, 1911) suggest that the chemical factor may also play a part in controlling the length of the digestive tract. The environment affects the digestive processes of Amphibia directly. M tiller (1922) has shown that the digestive action of the frog pepsin increases with rising temperature reaching an optimum at 40°C, a temperature at which few frogs will survive. Thus the optimum conditions for digestion are not the best temperatures for the health of the frogs. Amphibia are able to with
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Keywords: ., bookcentury1900, bookpublishernewyorkmcgr, booksubjectamphibians
