ORDER LEPIDOPTERA 



57 



quadrangular plates convex on the exterior concave on the 

 interior side, maxillae with well developed palpi and a 

 labium or lower lip also with palpi, — from this condition it 

 is a far cry to the mouth parts of the feeding stages of 

 Phylloconistis and the early instars of Gracilaridae. 



The difference consists not only in the different size, form, 

 and degree of development, but in the apparent presence or 

 absence of some of the organs themselves. Here the 



Fig. 23. Mandibles of leaf-mining caterpillars. (After Traegardh.) 

 A, Tischeria; B, Nepticula; C, Cnemiostoma; D, Parornix; E, Lithocol- 

 letis; F, Phyllocnistis. 



mandible becomes an extraordinary structure, looking 

 considerably more like a circular saw and working in a way 

 more similar to that of a saw than of an ordinary mandible. 

 Here it is a flat disc hinged at its proximal border and work- 

 ing to and fro in a horizontal plane. Enclosing the mandi- 

 bles are two thin flaps. The one that is above is the 

 labrum considerable enlarged, the one below is similar to it 

 and is made up for the most part of the maxillae, labium 



