PLATE 1 



EXPLANATION OF FIGURES 



Fig. 1 The horned toad on the right has become pale after having been kept 

 on a substratum of sand for six weeks. The other animal, as a result of having 

 been kept upon a substratum of cinders, has retained the dark color shared l^y 

 both at the beginning of the experiment. X 5i- 



Fig. 2 A pair of horned toads, similar to those of figure 1, photographed upon 

 the backgrounds on which they have been kept. X ^4. 



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