TO THEIR SURROUNDINGS 65 



surrounding surfaces. He has been able to obtain 

 almost at will chrysalids of different colors, accord- 

 inu: to tlie tints with which he has surrounded 

 them, and so has opened a new field of experimental 

 inquiry which may yield important, as it already 

 has interesting results. By carefully selecting the 

 time at which his experiments were made he has 

 been able to determine that in all the species 

 expermiented upon it was only necessary to con- 

 fine attention to that period in the later larval life 

 of the insect, when it has ceased feeding and 

 remains motionless, together with the early portion 

 of the next period, after spinning the silken pads 

 and shrouds for the pupal attacliments until it has 

 thrown off the larval skin. It had already been 

 pointed out by Meldola that it was impossible to 

 suppose the moist skin of the freshly formed pupa 

 photographically sensitive to the color of the sur- 

 rounding surfaces, and this has been made per- 

 fectly evident from the experiments of Poulton, 

 which show that the color is determined before the 

 assumption of the pupal state, since experiments 

 made later than the tmie mentioned produced 

 absolutely no results. Neither was Poidton suc- 

 cessfid, as he seems to have expected to be, in 

 preventing the influence of surrounding objects 



