144 CALIFORNIA ACADEMY OF SCIENCES. 



tallic or iridescent, while bluish-black or bluish gray is 

 present in thirty-five other genera, giving a total of 

 something like fifty-one genera with blue pigment. 

 Purple is by far the rarest of the colors, only six genera 

 showing it pure and seven in combination, while out of 

 these thirteen instances it is iridescent in ten. Gray 

 and brown are the most difficult colors to assign to a 

 given number of genera, because they frequently occur 

 only in the young, while in a large, number of instances 

 the two hues are more or less combined. In general, 

 however, it may be said that gray occurs pure in a hun- 

 dred and thirteen genera, and in combination in thirty- 

 nine others, making a total of a hundred and fifty-two. 

 Brown is found pure in a hundred and twenty-nine in- 

 stances, while in combination it exists in forty-three 

 additional genera, — a hundred and seventy-two in all. 

 These somewhat dry statistics of the relative abundance 

 of the different colors may be shown more clearly in the 

 following condensed table: 



Total number of genera 209 



Brown 172 Yellow 79 



White 169 Blue 51 



Gray 152 Green 30 



Black 135 Orange 10 



Red 116 Purple 3 



The above facts are susceptible of more than one in- 

 terpretation. The very large number of genera in which 

 brown is present may be accounted for by the fact that 

 brown affords better protection, and that where it ap- 

 pears it is a protective color which has been developed 

 by natural selection. The same argument might be ap- 

 plied to gray, while black and white usually occur in 

 such limited areas that they may be looked upon simply 

 as recognition markings. There is, however, another 



