52 ANIMAL COLORATION". 



species." It looks very mucli as if this change, which is one 

 of the most remarkable among those, which have been recorded, 

 were due to food ; but it is possibly a question of climate. 

 In any case it seems evident that the action of the environment 

 is the cause. 



The common garden snail ( Heli.r aspet^sa) is said to become 

 darker when fed upon lettuce. 



The " Tiger moth" {Chelonia caja) whose caterpillar is the 

 familiar " Woolly -bear," is almost the classical instance of 

 the effects of food upon colour. It appears to be in any case a 

 most variable species ; the pages of the Entomologist and other 

 journals devoted to entomology contain numerous records of 

 varieties, some of which have been traced to food while others 

 have not a known history. The orange red of the hind wings 

 may be replaced by yellow, and the proportions of brown and 

 white in the fore wings are subject to immense fluctuation. 

 Eimer * quotes from Koch a number of colour changes which 

 accompany and are probably caused by a change of diet. 

 Thus, if fed upon lettuce, the white ground of the fore wings 

 predominates over the brown ; the precise contrary is produced 

 by feeding the larvse upon the leaves of the deadly nightshade ; 

 in moths bred from larvas which have been fed upon the 

 leaves of this plant the white becomes almost obliterated, 

 while the bluish marks upon the hind wings fuse together and 

 displace the orange yellow ground colour. Koch concludes 

 the ac(!Ount of his observations with the following remarks \ 

 " Must not similar processes occur equally, and even on a 

 larger scale, in the natural life of the countless forms of the 

 class in question ? When a great number of individuals 

 perish through an occasional scarcity of their proper food 

 plant, must not, nevertheless, considerable numbers survive by 

 • " Organic Evolution,'' p. 150. 



