84 THE WOODPECKERS 



trunk, clinging at ease in almost any position 

 except head-downward, and drilling incessantly 

 and at all seasons for grubs; he is a typical 

 woodpecker of the largest size, but his hind toe 

 and claw are, if anything, a trifle shorter than 

 his middle toe with its claw. He throws it out 

 and uses it as we have described, but it has not 

 that disproportion to the other toes which we 

 expected to find as the result of a strictly arbo- 

 real life. 



What have we proved ? We have not shown 

 that the long toe is not more useful than the 

 shorter one, that is a matter of observation ; 

 but we have failed entirely to show that it is so, 

 and this can be done only in one of two ways : 

 either by proving that the logcock's habits are 

 not what all previous observers have believed 

 them to be, which would be assuming a great 

 burden of proof ; or by demonstrating that his 

 ancestry explains why his feet do not illustrate 

 our theory, and this, though it is undoubtedly 

 the true solution, could be settled only by a very 

 learned man. 



But we have encountered one truth which 

 must always be held in mind in science that 

 a theory is not proved while a single fact re- 

 mains rebellious and unsubdued. We might 

 have examined every other woodpecker in the 



