132 THE UNIVERSE. 



Many insects do even more to protect their metamorpho- 

 sis ; they envelop themselves in a mantle of silk, which pre- 

 serves them from the assaults of the rain and cold. In 

 certain butterflies it is evident that this covering is so ar- 



67. Larva and Nymph of the Panorpis, much enlarged, showing in this Fly the passage 

 from one state to another. 



ranged as to fulfil this double task : a dense external tegu- 

 ment, similar to the straw thatch of our houses in the coun- 

 try, allows the storm to pass over without penetrating ; 

 another, internal and softer, defies the cold of winter. 

 Buried at autumn tide in this double shelter, the butterfly 

 securely awaits the coming of spring to be born again. 1 



1 It is the cocoon or silken covering spun by the bombyx of the mulberry- 

 tree that furnishes our silk, such a well-known source of our industrial wealth. 

 Boyle, the chemist, relates that a lady, having taken the trouble to unravel a co- 

 coon of silk very carefully, and to measure the thread, found that it was more 

 than 300 English leagues in length. Boyle, Subtilty of Effluvia. Lyonet, with 

 much reason thinks there must be some mistake here. He found this thread to 

 be only from 700 to 900 feet long. 



