EVOLUTION OF THE COLORS OF BIRDS. 189 



important one. Can any law of growth be suggested, 

 for example, for chopping off a black line right through 

 the middle of the ear coverts as in fig. 3a, b and d, 

 and fig. 10* ? By attentively following the arrows, it 

 will be seen how either by the modification or combina- 

 tions of patterns, or both, each form may be derived 

 from some preceding form, more or less completely. 

 Figs. lOe, lie, d, e, alone fail to be reduced to a com- 

 munity with the other patterns. It is unnecessary to 

 encumber the text with the names of the various species, 

 which are not essential to the point under consideration, 

 and may be found in the explanation of plates. A few 

 words should be added concerning the nature of some of 

 the relationships here indicated. By a reduction of the 

 posterior extent of the black cap in fig. 1, fig. la is pro- 

 duced. A continuation of this reduction would lead to 

 fig. 16; while the cutting off of the front of the black 

 cap would give fig. Ic, which process continued would 

 end in fig. Id. Fig. 2a is hardly more than a narrow- 

 ing of the band of fig. 2, but fig. 26 is a combination 

 of this with fig. 16. In fig. 2c the band has become ex- 

 tended posteriorly abruptly downward, while in 2d 

 the angle is changed and it is extended not merely 

 downward but forward. 



It will not be necessary to, continue an interpretation 

 of all the transitions indicated in the diagram. I desire 

 simply to show that all the head markings of birds can 

 probably be interpreted as modifications of certain fun- 

 damental types which are probably the parent forms 

 from which all have sprung. They are in fact closely 

 allied to the primitive streaked plumage, and may be 

 looked upon as merely an aggregate of streaks in definite 

 parts of the head. 



It may now be more readily apparent why some forms 

 of marking never occur while others are so general. It 



