HEKEDITY, VAlUATiOiV 119 



in anv way selected as especially variable. It is a little larger 

 than our yellow-hammer^ and is therefore of a convenient 

 size to be shown on a diagram of its actual dimensions, thus 

 giving a better notion of the amount of variation of the several 

 parts than if reduced to a smaller scale. 



The vertical lines, numbered at top and bottom, 1-20, show 

 the measurements of the tw^enty specimens of this bird, and 

 the figures at the sides, 0-5, mark the inches. The specimens 

 are arranged in the order of length of body, shown by the 

 upper somewhat irregularly curved line of dots. This is seen 

 to vary from 4% inches to a little less than 5 inches. The 

 next lower line show^s the length of the wing of each specimen, 

 and we at once see the want of correspondence with that of 

 the body. ^o. 5, w^ith a quite short body, has the longest 

 wing of all; while No. 16, with a long body, has nearly the 

 shortest wing. The third line, showdng the tail-lengths, is 

 equally remarkable, for No. 6 shows the longest tail with quite 

 a short body, while No. 16, with one of the shortest tails, has 

 a long body; so that Nos. 6 and 16, measured in the usual way 

 to the end of the tail, would be found of exactly the same size, 

 though the one is really % inch shorter than the other. 



The next three lines show the varying lengths of the tarsus 

 (commonly termed the leg), the middle toe, and the outer toe, 

 and they too show very distinct and often contrasted divergences 

 in proportion to their small total length. Thus Nos. 11 and 18 

 have nearly the shortest legs with large bodies. The middle 

 toe in 7 is as long as in 19 and 20, while the outer toe is 

 decidedly longer than in 19, and in 12 decidedly shorter than 

 in 2. 



It is particularly important to note here that this remarkable 

 amount of variation occurs in only tw^enty birds taken at 

 random. But the species is one of the most populous in North 

 America, occurring in enormous flocks over the whole conti- 

 nent, from 54° N. lat. in summer, and migrating as far south 

 as Paraguay in winter. There must, therefore, be an average 

 population of (probably) hundreds of millions, giving a much 



