216 CALIFORNIA ACADEMY OF SCIENCES. 



2, where the adults are alike, but the young have a 

 peculiar first plumage. The following is a list of North 

 American species coming under this class: 



Merula migratoria. ' Chelidon erythrogaster . 



Myadestes toiunsendii. Tachycineta. 



Helminthophila swainsoni. Chondestes. 



Helminthophila ruficapilla. Spizella. 



Helminthophila Virginia?. Junco. 



Helminthophila lucice. Amphispiza. 



Dendroica nigrescens. Peucma. 



Seiurus. Pipilo. 



Lanius. Tyrannus. 



Ampelis. Melanerpes erythrocephalus . 



Petrochelidon lunifrons. Malanerpes torquatus. 



Among the species in this list no little variety and 

 specialization of color and markings is to be met with. 

 These are the forms in which the female has caught up 

 with the male, which originally led in the evolution of 

 color, or else species in which the colors of the two sexes 

 evolve pari passu. It is difficult to decide in which class 

 to place many of the above species, although where the 

 colors are very elaborate and decorative, as in the wax- 

 wings (Ampelis), the red-headed woodpecker (Melanerpes 

 erythrocephalus), and the violet-green swallow (Tachy- 

 cineta thalassina), it is safe to assign them to the former 

 category, whereas, when the colors are obviously of 

 use for purposes of recognition, as with the wag-tails 

 (Seiurus), butcher birds (Lanius), lark-finch (Chon- 

 destes), and Junco, the latter alternative is a possible 

 one. Still, the colors of the genus Pipilo are largely re- 

 cognition marks, and yet the female of the common 

 towhee of the Eastern States (Pipilo erythrophthalmus) is 

 colored differently from the male, although in. the very 

 closely related P. mo.culatus group the sexes do not dif- 

 fer. This seems to show that the characters of the genus 



