Grovjth and Metamorphosis of Tadpoles. 



299 



GRAMS 

 2-0 



1-5 



Days of Experiment 

 8 15 



S3 



0-5 



COD-LIVER OIL 



Fig. 4.— Showing the effects of 0"5 mgrm.' and of 1 ragrm. of iodine in accentuating the 

 retardation of growth induced in tadpoles by an excess of cod-liver oil in their food. 

 Dotted line shows the normal rate of growth of tadpoles receiving 1 mgrm. of iodine 

 per gramme of basal diet, but without cod-liver oil. 



(9) The iodine was added in solution of which the following is the com- 

 position : iodine, 0'477 grm. ; potassium iodide, 0'682 grm. (equivalent to 

 '0"521 of iodine) : water, 100 c.c. The iodine solution was intimately mixed 

 with the fat in each case, and the flour-caseinogen mixture subsequently 

 added to form the soft pills. 



(10) Food intake : The tadpoles ate the food-mixtures with avidity during 

 the earlier part of the experiment, and during this period the rates of growth 

 varied in a conspicuous way (fig. 1). Later, however, certain differences 

 in the food intake in different dishes were observed. Tadpoles receiving the 

 basal diet without admixture with fats, ate well throughout the whole course 

 of the experiment, so also did those receiving food-mixtures containing arachis 

 oil. Those receiving cod-liver oil and linseed oil ate greedily at first and 

 later much more sparingly ; while those receiving the harder oils, butter, 

 cocoa-nut oil and lard ate moderately, as did those receiving oleic acid 

 mixtures. It is concluded, therefore, that whUe the wide variations in the 

 rate of growth (fig. 1) between tadpoles receiving no fat and those receiving 

 fat may, in some measure, have been due to a lesser food intake by the 

 latter during the later stages of the experiment, the great retardation of 

 growth induced by the fat was not due in the main to this cause. 



(11) Temperature conditions — which have been shown by Julian Huxley 



