I. TRÄGÅRDH, LEPIDOPTEROUS LEAF-MINERS. 9 



free, and only its dorsal hind margin is overlapped by the 

 edge of the prothorax. 



While discussing the retraction of the head of the tissue- 

 feeders in the prothorax, it was pointed out that this was 

 due to the fact of the dorsal side of the head being consi- 

 derably longer than the ven trål one, and that, when the head 

 became horizontal, the dorsal edge had necessarily ' to be- 

 come embedded in the prothorax. 



It is, however, probable that the retraction of the head 

 involves a certain height of the prothorax, which would not 

 be desirable for a sap-feeder, where a thin wedge-shaped 



Fig. 5. Head capsule of Lithocolletis, dorsal aspect. X 206. 

 Fig. 6. » » » Phyllocnistis , » » X 70. 



head, with a smooth, härd surface, is a necessary feature. 

 There is a way out of this difficulty and that is to lengthen 

 the ventral side of the capsule; and it is this we notice in 

 the sap-feeders. The details of the head capsule will be 

 discussed in the following. 



Another feature is, that the oval outline of the head is 

 completely abandoned. In all species exainined the lateral 

 margins of the head are almost straight, and converge an- 

 teriorly in such a manner that the greatest width is at the 

 hind margin, the smallest at the base of the antennse, a 

 feature which, in connection with the anteriorly downward 

 sloping dorsal surface of the capsule, makes it an ideal wedge. 



