294 STUDIES, SCIENTIFIC AND SOCIAL 



0-56 inch in length, and from O'SO to 0-38 inch in width. 

 In the Yellow-crowned Warbler {Dendrceca coronata) the 

 quills vary in proportionate length, so that the first, the 

 second, the third, or the fourth, is sometimes the longest ; 

 and a similar variation of the wing, involving a change of 

 proportion between two or more of the feathers, is recorded 

 in eleven species of birds. Colour and marking vary to a 

 still greater extent. The dark streaks on the under parts 

 of the American Song-sparrow (Melospiza melodict) are 

 sometimes reduced to narrow lines, while in other speci- 

 mens they are so enlarged as to cover the greater part of 

 the breast and sides of the body, sometimes uniting on 

 the middle of the breast into a nearly continuous patch. 

 In the small spotted Wood-thrushes (of the sub-genus 

 Hylocichla) not only does the general tint of different 

 parts vary greatly, but this is accompanied by great 

 variation in the markings, some specimens being very 

 pale with in distinct narrow lines on the breast, while others 

 have dark plumage and dark, broad, triangular markings. 

 It must be remembered that all these differences are in- 

 dependent of those due to age, sex, season, or locality, and 

 consist solely of what may be termed the normal indi- 

 vidual variation of the species. 



It is, however, often supposed that variations occur at 

 any one time in single characters only, all the rest remain- 

 ing invariable ; and it is objected that to adapt a creature 

 to new conditions it must be modified in several ways at 

 once. But a reference to the tables given by Mr. Allen 

 shows that this coincident variation of several characters 

 does exist to a remarkable extent. He has given the 

 variation of no less than nineteen characters in ten species 

 of birds, from a comparison in each case of only twenty 

 specimens, all of the same sex, all fully adult, and all taken 

 in the same localities. On marking the specimens which 

 have each character at a maximum or minimum develop- 

 ment, we find the most curious combinations. We find, 

 for example, that the largest specimens have not always 

 the longest wings or tails, or the smallest specimens the 

 shortest ; the proportion of the different parts of the wing 

 varies quite regardless of the actual dimensions; the 



