234 ROMANCE OF THE INSECT WORLD CHAP. 



stance of another colour, known to produce an opposite 

 effect upon the pupa, leaving the rest of the company 

 on the accustomed site. The pupa taken, like the 

 pupae left, resembled the larval surroundings, and not 

 the subsequently chosen surface. Clearly the 

 surroundings had exercised their influence ere the 

 pupa was removed. 



So much certain, Mr. Poulton 1 had now to ascertain 

 the exact period of susceptibility to surroundings of 

 these organisms.* He first aimed at making careful 

 note of everything that happens to a caterpillar 

 between the cessation of feeding and the change to 

 pupa, for he felt sure that the time of susceptibility 

 lay somewhere within these limits. When the cater- 

 pillars with which the experiments were conducted are 

 full-fed, he tells us, they descend from the food-plant 

 to the ground, and wander about in search of a 

 surface on which to pass the pupal life. This Mr. 

 Poulton denominates stage I. Having selected the 

 spot the insect rests motionless upon it stage II. 

 Lastly the larva suspends itself head downwards 

 stage III. At the end of this time the skin 

 splits, exposing the chrysalis which eventually 

 generally gets rid of the now useless larval skin. 

 Stage I. seemed to Mr. Poulton to be out of count as 

 the period in question, since even if the caterpillars 

 were then susceptible, " no effective results could be 

 obtained ; for they are then wandering over surfaces of 

 various colours, of which few can be the same as that 

 which will form the environment of the chrysalis." Mr. 



1 I am indebted to Mr. Poulton's Colours of Animals for this 

 account of his researches. 



