METAMORPHOSIS OF AMPHIBIAN ORGANS 245 



animal, two and one-half months later, when the animal was 

 fully metamorphosed, only 32 spots were left. 



Figure 4 shows the separation of the network at a later period 

 on a worm-fed animal which left the water eleven days before it 

 was photographed and painted. This picture also shows that the 

 development of the spots on the tail has progressed more rapidly 

 than on the body. We shall refer only to the spots on the body 

 and head. 



The last stage which we call 'black' is reached when the 

 colors of the spots and background have fully cleared up. It 

 corresponds with the termination of metamorphosis. The 

 background then appears black and the spots are of a varying 

 bright yellow; the colors also are more vivid because the sur- 

 face of the skin is now glossy instead of dull. The transition 

 from the third into the last s'tage occurs very gradually and 

 no definite line can be drawn between them. Figure 14 shows a 

 fully metamorphosed animal. 



In the following text the terms 'cinnamon' and 'brown' refer 

 to the color of the background after the animal has left the water. 

 In the beginning it very often assumes a reddish brown color 

 which is called 'cinnamon' ; then this color changes into a green- 

 ish black-brown which is called 'brown'. By getting gradually 

 darker and darker this color becomes 'black.' 



It should also be mentioned that the rest of the skin in which 

 the network and the spots seem to be imbedded, is called "Back- 

 ground." 



Finally it must be said that size and shade of the yellow spots 

 varies greatly as we shall see later on, when we shall deal with 

 this fact. One exception should be mentioned here. A very 

 small percentage among a certain number of animals does not 

 develop any spots at all on the back, or only very few of small 

 size and of a faint greenish color. They seem to consist of a 

 number of tiny yellowish pigment dots, which attach a loose 

 aspect to them; they are called 'dotted spots.' In such animals 

 the rate of development of the background is more rapid than 

 the development of the yellow spots; at a similar stage of de- 



