1885.] Colouring of Phytophagous Larvae. 305 



Food-plant. 



Effect on S. Ocellatus. 



Colour of undersides 

 of leaves. , 





likely that the opposite effect may 

 be produced when the leaves are 

 downy and white underneath. My 

 experiments produced intermediate 

 forms, but they are not very con- 

 clusive, for the larvae could not be 

 fed upon the same variety of S. Ci- 

 nerea, as I was travelling about at 

 the time. On some occasions I was 

 obliged to use leaves with white 

 pubescent undersides, which I believe 

 tend towards whitish-green. 





S. Triandra . . . 



Mr. Meldola's instances (about 19) point 

 towards the tendency being in the 

 direction of whitish-green. My own 

 experiments upon the modifying 

 effect produced upon the whitish 

 larvae by feeding on this plant 

 throughout the fifth stage, rather 

 tend towards the other direction. 

 From the colour and surface of the 

 leaves, I should certainly have 

 thought that the tendency is strong- 

 ly towards yellowish. 



Undersides green and 

 glabrous. 



S. Babyloniea. . . 



Of seven instances, one was yellow and 

 six intermediate, inclining towards 

 the yellowish side. The former I 

 believe represents the tendency of 

 these leaves, which much resemble 

 those of S. Rttbra. 



Undersides green and 

 glabrous. 





A fair number of instances in favour of 

 a very strong yellowish tendency. 

 Only one exception (intermediate). 

 Experiments confirm the observa- 

 tions, as yellowish intermediate 

 forms were produced from larvae, 

 strongly tending towards the whitish 

 variety. 



Undersides green and 

 glabrous. 



Looking at the above list, I am strongly convinced that the ten- 

 dencies of one of the food-plants of this larva can be ascertained by 

 looking at its leaves, and that leaves with white pubescent under- 

 sides, as a rnle, produce whitish varieties, while those with green 

 glabrous undersides generally produce yellowish forms. 



The greatest support to the theory that the colour and texture of 

 the undersides of leaves is the best criterion of the effects is shown 

 by the very strong cases of apple and 8. Rubra. The same theory is 

 supported by crab, 8. Cinerea, and 8. Ferruginea, as far as their evi- 

 dence goes, and S. Smithiana is certainly not in opposition to it. 8. 



