PLATE 13 



Fig. 20. Nest of the Lucy warbler {rermivora luciac) in crevice on side of 

 trunk of partly dead ironwood shown in plate 12, figure 19. This nest contained 

 three eggs. Photographed April 12, 1910, on the California side, eighteen miles 

 above Picacho. 



Fig. 21. Selected specimens of Mephitis estor from the Colorado Valley: 

 at left, no. 10575, Chemehuevis A'^alley, California side; middle, no. 10574, five 

 miles south of Needles, California side; at right, no. 10579, twenty miles above 

 Picacho, California side. The variation shown is individual. If the contrasted 

 black and white markings are of warning signficance. hence of adaptive advan- 

 tage to the species, why should the desert skunks have proportionally much 

 more white than skunks from the humid northwest coast belt of the United 

 States? (See text, p. 256.) 



[294] 



