ON VARIATION. 



39 



demonstrates the following points. First : the color- 

 variation is determinate and not indeterminate. It 

 consists in, a, the successive enlargement of the dorsal 

 spots toward, to, and across, the belly; b, the diminu- 

 tion and extinction of the longitudinal stripes on ..the 

 head ; c, do. of the spots of the inferior surface of the 

 body ; d, in the increase of red in the color of the 

 dorsal spots, coincidentally with the changes men- 

 tioned. Second : these color-changes follow parallels 



polyzona 



conjuncta 



gentilis 



annulata 



parallela 



syspila 



doliata 



collaris 

 clerica 



I 



triangula 



of latitude, the red color and accompanying changes 

 developing from north to south. Third : so far as re- 

 gards eastern North America, there is a diminution of 

 size in passing from north to south ; the O. d. coccinea 

 being the smallest of the subspecies. In Mexico, the 

 size is recovered, as the O. d. polyzona equals in di- 

 mensions the O. d. triangula. 



The young of the northern O. d. triangula pre- 

 sents the colors of the dorsal spots nearly as brilliant 

 as those of the southern O. d. coccinea, and they fade 



