170 CALIFORNIA ACADEMY OP SCIENCES. 



all colors were produced strictly in accordance with 

 these laws and utterly regardless of any external in- 

 fluences which might modify the patterns. We must, 

 however, frankly acknowledge that, while all internal and 

 constitutional laws of development must rigidly limit 

 and condition the assumption of pigment by a feather, a 

 large proportion of color markings are produced by ex- 

 ternal causes — natural and sexual selection, direct action 

 of the environment, etc. For example, the general laws 

 of the location of growth force might have caused the 

 pigment to have lodged in the tips of the feathers of the 

 thrush's breast, but the effect would have been one of 

 mottling. Then natural selection might have taken 

 advantage of this and emphasized and defined the mark- 

 ings, and left each one distinct and isolated as a spot. 

 And thus it is with the wing bars and bands under con- 

 sideration. They have doubtless been produced by 

 selection for some effect, and indeed it might be argued 

 that the orderly sequence from feather to feather was 

 due solely to the fact that in this manner the general 

 effect might best be secured. This view, however, can, 

 I think, easily be shown to be untenable. For example, 

 upon the last primary of a wing of the Californian wood- 

 pecker {Melanerpen formicivoriis bairdi), which I ex- 

 amined, was a mere suggestion of a white dot below the 

 strip of white on the inner side of the feather. It was 

 so small that it might easily have been overlooked in an 

 examination of the feather, and most certainly could 

 have had no more influence on the general appearance 

 of the feather than a speck of dust. Upon the feather 

 next it, the first secondary, a well marked spot appears 

 in exactly the same place, while in the secondaries suc- 

 cessively following the first this spot slowly dwindles 

 away. Now it might of course be argued that this spot 

 had been a useful character at some past time, but was 



