38 



THE AMEBIC AN NATURALIST [Vol. XLIT 



cession, in the case of the tanager, of scarlet— green, scar- 

 let—green, year after year, but that it may be inter- 

 rupted by certain external factors in the environmental 

 complex. 



The further significance of these results I leave to 

 others, or until I have more complete data, checked by 

 results derived from control of the other factors of the 

 environment. It would be worse than useless to formu- 

 late any theories at the present incomplete stage of the 

 experiments. 



The scarlet tanager is of especial interest, as I have 

 said, on account of the absence of such an annual change 

 of color in its near relative, the summer tanager, and 

 experiments with the latter species may shed some light 

 on the subject. Other experiments concerning half and 

 even quarter moults are yielding interesting results and 

 will soon be reported upon. 



There is a great satisfaction in thus making even the 

 merest beginning at threshing out these problems, which 

 in their general evolutionary aspect are of far wider 

 application than in the Class Aves alone. And work 

 along these lines is all the more enjoyable because it 

 entails the loss of no life as concerns the birds themselves. 



