292 



THE EFFECT OF FOOD 



green external leaves. These larvse, however, were all 

 of a bright green or brown colour. Hence it would 

 seem that both etiolin and chlorophyll are capable of 

 being transformed into a larval colouring matter, which 

 may be either green or brown. 



As regards the effects of feeding among vertebrate 

 animals, a careful series of experiments upon tadpoles 

 (Rana esculenta) has been made by Yung.* The tad- 

 poles were all derived from the same batch of eggs, and 

 were placed, in groups of fifty, in six similar jars of 

 water. All the conditions of development such as 

 light, temperature, and frequency of change of water, 

 were identical, the food alone being varied. The kinds 

 of food supplied, and the average size attained by the 

 tadpoles after 42 days' development (three being meas- 

 ured in each case), are given in the accompanying table: 



Here we see that the purely vegetable diet acted least 

 favourably, and the beef diet the most favourably. 

 Egg yolk did not answer so well as coagulated egg al- 

 bumen, but better than uncoagulated albumen. From 



* Arch, de Zoologie Exper., 1883, p. 3. 



