VARIABLE PROTECTIVE RESEMBLANCE IN INSECTS 127 



not cause nearly such strong effects as the gilt sur- 

 roundings. The tendency was evidently hereditary 

 and shared by all the caterpillars of the company, so 

 that we have a striking example of the errors which 

 were eliminated by keeping the companies separate. 



It is almost unnecessary to point out how com- 

 pletely the old theory of * photographically sensitive ' 

 chrysalides is broken down by these experiments. 

 Not only is the adjustment of the pupal colours to 

 their surroundings due to larval susceptibility, but 

 the larva itself has ceased to be highly sensitive many 

 hours before pupation takes place. And this is to be 

 expected, for during the latter part of stage iii. rapid 

 changes are going on beneath its surface, and the 

 developing pupa is becoming loosened from the larval 

 skin which encloses it like a shell. Putting together 

 the results of all the experiments, it is probable that 

 in this species the influence of surrounding colours 

 operates upon the larva during the twenty hours 

 immediately preceding the last twelve hours of the 

 larval state. Hence stage ii. is the great period of 

 susceptibility, and this is probably the true meaning 

 of the hours during which the caterpillar rests motion- 

 less on the surface upon which it will pupate ; while 

 stage iii. has other meanings connected with the rapid 

 pupal development which is taking place. 



