hfUTBITION AND GROWTH OF LARVAE 



155 



The larvae may be carried to and through metamorphosis (Anura) which takes 

 from 2i months to longer, depending upon temperature, space, and food. 

 In this experiment, with temperature and space controlled, the emergence of 

 the forelimb can be regarded as the beginning of metamorphosis and a ter- 

 minal point for the nutrition experiment. 



OBSERVATIONS AND EXPERIMENTAL DATA: 



Growth measurements should be taken at weekly intervals to determine the relative value 

 at different stages of the different nutritional offerings. These readings may be taken 

 rapidly by placing a piece of calibrated graph paper beneath a Petri dish, and the tadpoles 

 transferred to this dish for direct size readings. 



DISCUSSION: 



Feeding of amphibian lar'vae is not necessary for several days after the mouth opens as 

 there is at that time still some reserve yolk which can be utilized. For the Anura feed- 

 ing may begin at stage #25 and for the Urodela at stage #40. A varied diet is generally 

 considered the best, and the Anura are thought of as herbivores and the Urodeles as 

 carnivores, although they may both be omnivores. Certainly the frog tadpoles, when 

 they are short on rations, will eat dead tadpoles, worms, and other organisms. In fact, 

 there is some evidence of cannibalism among the frog tadpoles. The elongated intestine 

 of the Anuran tadpole is associated with its vegetarian diet and those forms raised en- 

 tirely on a protein or non-vegetarian diet tend to have shorter intestines. 



The Anura do better on food with a green color while the Urodela do better on living, 

 moving food such as Daphnia, worms, and small tadpoles. When crowded and underfed, 

 the Urodela will snip off each others tails, and growing appendages. 



TABLE 1 



Incidence of kidney stone in tadpoles reared on spinach and 

 non spinach diets. See text for more detailed explanation. 



From Briggs G Davidson, 1942: Jour. Exp. Zool 90:401 



