METAMORPHOSIS OF AMPHIBIAN ORGANS 247 



Such yellow dots may be detected occasionally even in adult 

 individuals. 



On examination with a high power binocular lupe the phenom- 

 enon described above appears somewhat different. From the 

 beginning a small number of contracted melanophores can be 

 seen scattered throughout the yellow iris. The darkening of 

 the iris is not due so much to an accumulation of melanophores 

 the number of which increases very little, but to the appearance 

 of orange or reddish yellow blots. In these blots the blood can 

 be seen circulating while in the early stage the blood circulation 

 could not be seen. It also seems that some of the yellow chro- 

 matophores themselves have become somewhat darker yellow. 

 In the very early stages a division into two sections can be seen — 

 an inner narrower section and an outer wider section. The 

 inner section does not contain any melanophores at all and ap- 

 pears even under a weak magnification of the microscope as a 

 continuous ring of pure yellow pigment (fig. 5). This division 

 into two sections later on becomes more accentuated as the red- 

 dish yellow blots only appear in the outer section. Finally, 

 in the outer section the amount of darker pigment increases and 

 large parts of it appear brown while the inner section still re- 

 mains without melanophores. It is at this time that to the 

 naked eve the ring seems to have become narrower since the 

 outer section has become black to the naked eye. At the time 

 that the naked eye sees the breaking up into black and yellow 

 dots, the yellow chromatophores of the inner section have started 

 to loosen up and form — by means of their anastomosing processes 

 — a fine network through the meshes of which the black epithelial 

 layer of the iris seems to become visible. Soon the yellow 

 chromatophores become fewer and cease to anastomose with 

 each other. This process and a gradual decrease in the number 

 of isolated yellow chromatophores correspond to the decrease 

 in the number of yellow dots seen by the naked eye ; each yellow 

 dot corresponds to one single xanthophore (fig. 6). 



The stage of breaking up into yellow and black dots will be 

 assumed to be the beginning of the eye's metamorphosis. 



