All illustrations taken from living tadpoles. All figures in natural size except 

 figures 10, a to i and 11, a to /. 



PLATE 1 



EXPLANATION OF FIGURES 



1, a to ze Rana temporaria I. Experiment I. a, liver; b, spleen; c, thymus; 

 d, muscle; e, ovary;/, adrenal cortex; g, adrenal medulla; h, brain; June 6, 1912. 

 i, liver; k, liver-thjToid ; I, spleen; m, spleen-thyroid; n, muscle; o, muscle-thyroid ; 

 p, ovary; q, ovary-thyroid; r, adrenal cortex; s, adrenal cortex-thyroid; t, adrenal 

 medulla; u, adrenal medulla-thyroid; v, brain; w, brain-thyroid; June 26, 1912. 

 In k, m, 0, q, s, n, to, thyroid feeding had been started on June 17, 1912. x, liver; 

 y, brain; z, spleen-thyroid; za, muscle-thyroid; zb, ovary-thyroid; zc, adrenal cor- 

 tex-thyroid; zd, adrenal medulla-thyroid; ze, brain-thyroid, July 6, 1912. In z 

 to ze, thyroid feeding had been started on June 17, 1912. 



2, a to n Rana temporaria II. Experiment IV. a, original size, June 4, 

 1912. b, control; c, thyroid-muscle, thyroid given 1 day; d, thyroid-muscle, 

 thyroid given 3 days; e, thyroid-muscle, thyroid given 5 days; June 17, 1912. /, 

 thyroid-plants; thyroid given 1 day; g, thyroid-plants, thyroid given 2 days; /?, 

 thyroid-plants, thyroid given 4 days; i, thyroid-plants, thyroid given 5 days; k, 

 thyroid-thymus; I, thyroid emulsion; June 17, 1912. m, thyroid-thymus, w, thy- 

 roid-muscle; thryoid given 4 days; June 26. 



3, a to n. Rana temporaria III. Experiment III. a, thymus; b, muscle; c, 

 thymus-thyroid I; d, thymus-thyroid II; e, thymus-thyroid III; June 1, 1912. /, 

 thymus-thyroid II; g, thymus-thyroid III; h, thymus-thyroid IV; June 17, 1912. 

 i, thymus; k, thymus-thyroid V; I, muscle; m, muscle-thyroid; June 26, 1912. n, 

 muscle-thyroid; July 6, 1912. 



5, a to e Rana temporaria V to VII. Experiment VI. a, control; b, glandu- 

 lar hypophysis; June 26. c, control; d, glandular; e, neural hypophysis; July 6, 

 1912. 



6, a to d Rana temporaria V to VII. Experiment IX. a, control; b, thymus- 

 thyroid; June 17, 1912. c, control; d, thymus-thyroid; June 26, 1912. 



474 



