142 LEAF-MINING INSECTS 



a rule without leaving their cases, by reaching through a 

 hole in the epidermis, and feeding in a circle as far as they 

 can reach while holding on to their cases in the rear. 



Hence, they are ordinary little caterpillars in form, all 

 tissue-feeders, not flattened, nor otherwise specially adapted 

 to leaf-mining. 



In development the many species are similar. Of those 

 having a single generation a year, the eggs are laid in summer; 

 the larvae feed and make small cases in which they hiber- 

 nate; in early spring they feed again for a few weeks; sealing 

 down their cases, they transform to pupae; and the adult 

 insects issue in late spring or early summer. In those that 

 have two generations a year one set of larvae hibernates in 

 a similar way. 



The egg. The eggs are never inserted within the plant 

 tissue, though in some seed-and-flower-feeders they are 

 slipped inside unopened florets. They are deposited on 

 the leaf surface. Among the leaf miners of the group there 

 are at least two types of eggs and two modes of entering the 

 leaf, as described under the two illustrative species cited 

 in the following pages. 



The larva. The larva (see pi. 2, figs. 7 and 8) are little if 

 at all depressed. The head capsule differs from that of 

 most miners in that the front is not open, the arms of the 

 epicranial suture meeting the stem about a third of the way 

 from the vertex. The adfrontal plates extend to the vertex. 

 The ocelli are all close together. The body is nearly cy- 

 lindrical. The thoracic legs are well developed and strongly 

 chitinized. Prolegs occur on segments 3, 4, 5, 6 and 10 of 

 the abdomen. These protrude but slightly, and are to be 

 found close to the middle line of the ventral surface so that 

 the hooks, which are in two transverse rows on each proleg, 

 form nearly continuous bands across the central part of the 

 venter. The anal prolegs are better developed than the 



