294 THE LIFE OF AN INSECT. 



knows well to find them. This case is heavier 

 than water, and consequently cannot float, and so 

 carry the insect to the surface. As the insect 

 enters the pupa state it weaves, at the entrance of 

 its singular habitation, a grating of silk, which, 

 strange to say, is not only not softened and melted 

 away by the water, but hardens under it until it 

 is as hard as gum. This little grating is of a cir- 

 cular form, and fits exactly into the opening, 

 and is perforated with holes, so as to look some- 

 thing like the gratings which cover 

 our coal-cellar mouths in the pave- 

 ment of cities. These holes are for 

 the purpose of letting in fresh water 

 for the respiration of the insect. 



Grating of the Pupa- ~ . 11 ,1 



case. (jut or this under - water cell the 



insect must make its escape. To enable it so 

 to do the pupa is furnished with two strong 

 curved jaws, which are of no other use than to 

 assist it in making an opening in one of the 

 silken doors of its case, as they are cast off im- 

 mediately afterwards, and there remains not a 

 vestige of them in the perfect insect. This open- 

 ing made, the pupa forces its way out at that 

 end. But what then? How is it to reach the sur- 



