56 LEAF-MINING INSECTS 



They are six in number, nearly uniform in size and arranged 

 in a more or less regular semicircle which is opened poste- 

 riorly and subventrally. The difference from this condition 

 is, in the leaf-miners, both in arrangements and number. 



In getting them nearly marginal, Laverna has five ocelli 

 in a rather straight line near the edge, with the foremost of 

 the five and a sixth one that is farther from this line on the 

 very margin. Cemiostoma has all six in a zigzag line on the 

 dorsal surface near the margin. Aphelosetia has but five all 

 very near the margin, three on the dorsal and three on the 

 ventral surface. In Tischeria eikbladhella all are in one row 

 but the three anterior ones and the three posterior are 

 grouped in sets. 



The tendency to reduction in number is carried further in 

 some species of Lithocolletis where in the young larvae five 

 of the six ocelli present are all much reduced in size. In 

 other species of this genus young larvae have but four ocelli. 

 In Eriocrania and Xepticula there is one large ocellus only. 



The antennae of leaf -mining caterpillars are reduced to a 

 greater extent than are those of external feeders. Traegardh 

 has traced the stages of their reduction pointing out that 

 loss in segments may begin at the proximal or distal end. 

 The antennae of tissue feeders are more reduced than those 

 of sap-feeders. This is doubtless correlated with the in- 

 sertion of those of the latter in the necklike constriction 

 between the head-capsule and the mouth parts. In these 

 lateral incurvations they are but slightly exposed to pressure 

 against the walls of the mines. 



Mouth parts. But if the effect of leaf-mining is impressed 

 on the form of body and the locomotor appendages, in the 

 shape of the head-capsule and its sensory organs, it is no- 

 where more apparent than in the mouth parts, especially 

 in those of the early sap-feeding instars of the Gracilaridae. 

 From the condition in ordinary caterpillars — a labrum 

 shaped as a transversal plate, mandibles as triangular or 



