188 CALIFORNIA ACADEMY OF SCIENCES. 



this marking is associated with other head markings, 

 or where it is present but not black in color. The fourth 

 type the malar steak, represented by Colaptcs auratus 

 in the plate, is less commonly met with alone; but type 

 5, Dendroica virens in the diagram, which is the throat 

 patch, is very common. There are only a few forms, 

 however, such as Dendroica occidentalis and Amphispiza 

 bilineata where it occurs as the only black patch upon 

 the head. 



The combinations of these five types follow next. Fig. 

 6 is Dendroica tigrina, which presents a combination, 

 not of types 1 and 2, but of 1 and modification a of type 

 2. Fig. 7, Dendroica blackburnia;, is a combination of 

 1 and 3, the black cap and ear covert. This is a very 

 common form, being presented with greater or less 

 deviation from the type by such forms as Sitta. can- 

 adensis, Certhiola bahamensis and Pitangus derbianus. Fig. 

 8 is the combination of types 1 and 4, as shown in 

 Dendroica striata. Fig. 9 is a combination of types 1 

 and 5 illustrated by Parus atricapillus. Fig. 10, of 

 Ampe.lis cedrorum is equivalent to 2a plus 5, and fig- 

 ure 11, Heiminthophila chrysoptera, equals 3 plus 5. 

 Fig. 10, Parus hudsonicus, is a combination of types 

 1, 2 and 5; while fig. lla, Mniotiita varia, is a com- 

 bination of types 1, 3 and 5. 



There is little difficulty in understanding these types 

 and their combinations as markings which have fol- 

 lowed the feathers along natural areas of the birds' 

 heads. They may thus be in part accounted for in ac- 

 cordance with the location of growth force along lines of 

 least resistence, although natural selection has played a 

 not unimportant part in shaping and defining them. 

 Upon leaving the types and considering the various 

 modifications, it becomes immediately evident that here 

 the part played by selection must have been a far more 



