THE CUCKOO'S MATE 221 



daily for weeks before departure, fly through half the 

 longitude of the globe for their winter holiday and 

 their summer resting. 



To aid it in its creeping habits, the cuckoo's mate 

 is pencilled in the most marvellous way into an invisi- 

 bility that no one colour could give it Of course, it is 

 a wonderful scheme of protective colouring, and, in a 

 general way, we can see or feel how generations of 

 selection brought it about. But how, in the first place, 

 does the body of the bird achieve and keep constant 

 so intricate a pattern ? Says Mr. Pycraft, in his latest 

 book on the " History of Birds," in considering the 

 lines on an individual feather : " These lines are not 

 continuous, not organically complete, but formed by 

 the exact relation, one to another, of a series of minute 

 spots of pigment each lodged in a separate filament, 

 so that the several spots in each separate filament, 

 when ranged side by side, form the several series of 

 lines, straight or vermiculated, as the case may be." 



It is comparatively easy to understand a bird getting 

 blacker and blacker, or greener and greener, all over, 

 in response to the double call of the influence and the 

 needs of the environment, but not nearly so easy to 

 imagine how, when the delicate veinings of decayed 

 and cracking wood are to be imitated, determination 

 is come to as to which part of which feather shall 

 represent crack and which the grey of the smooth 

 surface. The dot on any given filament could, 

 obviously, form part of a longitudinal or a trans- 

 verse strip, of a complete circle or square, of a con- 

 cave or a convex design. When a striped bird 

 becomes a barred bird, as undoubtedly has happened 

 now and then, perhaps some pivotal dot remains, and 



