118 LEAF-MINING INSECTS 



vestiges and the prolegs showing as hardly more than a 

 circlet of crochets on the integument. 



The pupae of all the Gracilariidae have considerable 

 power of movement. If touched in their retreats a vigor- 

 ous reaction may be set up in which they bend the abdomen 

 and roll from side to side. When the adults are ready to 

 emerge they become active within the shells and force an 

 exit aided by the free segments in the abdomen, a cutting 

 crest or plate on the head and backward pointing spines. 

 When the pupal shell is pushed out far enough and comes 

 to rest on the leaf or cocoon surface with only the hinder 

 segments remaining in the emergence hole, then its skin 

 splits and the adult is freed. And often the adult is an 

 exquisite little creature, arrayed in shining scales and plumes, 

 its wings overlaid with glistening silver or burnished gold. 



The size of the family and the range of its food plants 

 will be learned by consulting our lists in Chapters XV and 

 XVI. They are so numerous that we can use but a few typi- 

 cal representatives of the principal genera for illustration. 



PARORNIX 



This is a genus of more than a dozen species of leaf -miners 

 that show a partiality for plants of the rose family. The 

 very young larvae of the genus Parornix mine by shearing 

 through the cell walls of a single layer of parenchymous 

 tissue nearest the cuticle. In this genus the lower side of 

 the leaves is the one attacked. Aiter assuming more nearly 

 normal head capsules and mouth parts at the second moult 

 they usually continue in the leaf for a while, picking out 

 the parenchyma from the exposed tissue. When nearly 

 grown they emerge from the leaves and feed within a shelter 

 made by turning and binding down the border of a leaf. 

 The fold made by members of this genus, unlike that made 

 by species of Gracilaria, is more often flat than cone-shaped. 

 In some such fold the cocoons are later spun though it is 



