12 ROMANCE OF THE INSECT WORLD CHAP. 



week or ten days. In every species the length is 

 much affected by the weather. Should a butterfly 

 larva turn to pupa during the summer, it may 

 become perfect in eight or ten days, but if it reach 

 the chrysalis state at the approach of winter the 

 change to butterfly may be delayed for months, until 

 development is quickened by the warmth of returning 

 spring. Reaumur discovered that if a chrysalis were 

 deposited in an ice-house, further transformation 

 might be retarded for two or three years. If one 

 deep in its winter sleep were brought in from the 

 cold to great heat, the final metamorphosis might 

 take place in ten or fourteen days. 



As the structures become completed, and the hour 

 for entering the imago condition draws near, the 

 immobile pupa begins to show signs of returning life. 

 In Sphinx respiration increases rapidly, twitchings 

 and contortions indicate what is about to occur, and 

 the form of the coming insect becomes more and 

 more apparent. In every instance the assumption of 

 the perfect state is accompanied by a casting of 

 the outer skin. Before this can be effected, many 

 insects have first to acquire the power of locomotion. 

 Caddis flies which undergo their previous metamor- 

 phoses in water, must be able to come to the sur- 

 face, or to quit an element in which they cannot 

 now exist. Pupae that are lodged in the interior 

 of trunks of trees, or in crop stems, or beneath the 

 ground, usually issue forth from these situations ; 

 and many Lepidoptera and others have to struggle 

 through silken wrappings. Having overcome the 

 obstacles that oppose its escape, the pupa bursts 



