AND OF LIGHT. 261 



larvae of Smerinthus, proved that it was the colour of 

 the leaves, and not their food quality, which provoked 

 the change. Thus he sewed leaves together, " so that 

 the caterpillars were exposed to the colour of the upper 

 or of the under side alone, although they ate the same 

 leaf in both cases. In other instances the bloom was 

 rubbed off the under sides of some leaves, whilst others 

 were left normal." 



More striking cases of protective resemblance were 

 obtained by Professor Poulton for various Geometra 

 larvae. Larvae surrounded by the leaves on which they 

 fed, became, in the majority of species, light brown or 

 light gray in colour. If, however, an abundance of 

 twigs had been mixed with the leaves of the food plant, 

 they became dark in colour. The larvae of the Pep- 

 pered moth (Amphidasys betularia) afforded the most 

 striking result of all, for when reared amongst green 

 leaves and shoots they became bright green without ex- 

 ception, whilst in the presence of dark brown twigs they 

 nearly all assumed a corresponding colour. 



The influence of the surroundings acts only very 

 slowly upon the colour of the caterpillars, the coloured 

 part being " actually built up of the appropriate tint." 

 Probably this is the result of light stimuli acting on the 

 surface of the skin, and not reflexly through the eye. 

 Thus painting the eyes (ocelli) with opaque varnish led 

 to no diminution of reaction. 



