936 THE AMERICAN NATURALIST. 
A word should be said here against too hasty conclusions on 
this subject of colors. Many species of crayfish are migra- 
tory in their habits. This is especially true of those living in 
running water. The changes in color require some weeks or 
possibly months of time. For these reasons the color of cray- 
fish seen in the small streams may not be at all like the color 
of the environment. The best results will be obtained from a 
study of the crayfish in the small ponds of water where migra- 
tions cannot occur. 
