OF THE UNITED STATES 281 



attitudes on the shelf bottom of their former home, I made the 

 photograph, a copy of which appears as one of the accompanying 

 illustrations. The birds shown in this picture I take to be about 

 ten or twelve days old, and it must be several days after this be- 

 fore any feathers begin to appear upon them. 



Later in the season my son found another nest of this species, 

 and from it succeeded in capturing a nestling that was just about 

 to shift for itself. Of this bird I succeeded in getting a number 

 of good photographs, and one of these is reproduced here, ex- 

 hibiting him in a peculiar attitude that he assumed when he 

 jumped from the horizontal part of a limb to another portion 

 growing out from it at nearly right angles. Coming to a rest 

 after this jump, he frequently held on to the bark with his foot in 

 the awkward manner illustrated in the picture shown on this 

 page. 



In closing this chapter I desire to say a few words about the 

 pterylography of woodpeckers, and were the question pro- 

 pounded to any person who had never given the matter a thought 

 are the feathers of birds implanted in their skin in such a way 

 as to spring from it by an even and unbroken distribution over 

 the entire surface of the body, or are the feathers arranged 

 upon any plan, so that were they all trimmed down close to the 

 skin there would be presented to us some definite pattern of ar- 

 rangement duly outlined by the remaining extremities of the 

 quill-butts? I am inclined to suspect that not only that person 

 but perhaps a great many people would at first say, " Why, a 

 bird's body is entirely covered with feathers, of course, and they 

 arise by an even distribution all over it." Now, the truth of the 

 matter is that there are but a very few birds indeed that at all 

 approach any such condition (penguins, toucans, and ostrich-like 

 birds), the vast majority of the class having their feathers ar- 

 ranged upon their bodies after some definite plan. This partic- 

 ular arrangement of a bird's plumage is technially designated 

 by those engaged in investigating their structure as its ptery- 

 losis. From the several parts of the body the feathers spring 

 from the skin along certain lines, or from definite circumscribed 

 areas, in either case known as " tracts " (pterylce), while the un- 

 feathered portions which occur in between these are defined as 

 "spaces" (apteria). Such being the case, science in due time 

 seized upon this discovery and enlisted so useful a character as 

 an aid to the classification of birds, as men were not long in find- 



