i8 



HOUSE, GARDEN, AND FIELD 



within 



and unprovided with a biting mouth, escape through the 



tough epiderm of the holly-leaf ? The aperture by which 

 the egg or the larva passed in was ex- 

 tremely minute, and is now choked up by 

 dead vegetable matter ; even if it remained 

 open, the fly would have to ramble up and 

 down in a very low passage, at the risk of 

 damaging its gauzy wings, in order to dis- 

 cover the way out. The problem is not to 

 be solved thus. Consider for a moment 

 how you would provide for such a diffi- 

 culty, if it had been left to you to arrange 

 the life-history of the holly-fly. Some 

 P e P le to whom the question has been 

 protectve offered as a puzzle, have found it too hard, 

 and nobody has succeeded who had not 



knowledge of the behaviour of other insects in like 



emergencies. Yet it is really as easy 



as making an egg stand on end. When 



the fly has come forth, you see a hole 



torn in the blistered epiderm, and in 



that hole the empty pupa-skin is left 



sticking. If we watch the leaves daily, 



we sometimes detect, not an empty 



but a full pupa-skin, still lodging the 



body of the future fly, and wedged in 



a good-sized hole. The last act of the 



larva, before it ceases to feed and move 



about, is to bite through the epiderm, 



and thus all the rest becomes easy. 



Do not fail to remark what we can 



hardly help calling the forethought of 



the larva. If it were to fail to force 



a passage beforehand, the future fly 



would be hopelessly imprisoned. Just 



in the same way a wood-boring larva comes to the outside 



of the tree-trunk, a leather- jacket (larva of daddy-long- 



FIG. 2. Pupaof holly- 

 fly removed from the 

 protective larval skin. 

 The ventral surface, with 

 the head , legs , and wings , 

 is seen. 



