286 CALIFORNIA ACADEMY OF SCIENCES. 



ready enunciated — the law of the assortment of pig- 

 ments, and the bleaching and intensifying of colors by 

 environmental influences. The original pigments of 

 the ancestral form were probably black and yellow. 

 These combined produced the olive green and brown so 

 common in this family, as in Tyrunnus verticalis, for 

 instance. By selection the pigments were separated to 

 a greater or less extent producing such specialized marks 

 as the black cap of Milvulus tyrannus, the black tail of 

 TyrannuH verticalis, the yellow crown patch of Tyrannus 

 tyrannus, etc., or in more diffused form the yellow ap- 

 peared on the belly as in Pitangus derbianus, or even 

 extended over the entire breast in a much richer shade, 

 as in Tyrannus mdancholicus coit-c/iii, and other tropical 

 species. The yellow has been both extended and in- 

 tensified by the influence of a tropical climate, while 

 from less determinate causes of intensification it has 

 been modified into its correlative red. As has been pre- 

 viously pointed out, the stages of intensification of the 

 yellow into red through orange, are shown in the crown 

 patch of the genus Tyrannus. A more complete transi- 

 tion of the yellow into red has occurred in the vermilion 

 fiycatcher (Pyxocephalus rubineus mexicoAius), in which 

 species it is to be noted that the red color occurs in the 

 same parts of the body that have a tendency to be colored 

 yellow in other genera, viz., on the top of the head 

 and under parts. 



Attention has already been called to Plate VI, as 

 showing the bleaching influences of an arid environment 

 on different species of the genus Myiarchus. In the 

 same manner, probably, the light gray and white of the 

 genus Milvulus has been largely produced. 



All the smaller flycatchers are to be regarded, it seems 

 to me, as degenerate descendants from some more brightly 

 colored race. They have been enabled to survive by 



