20 



ARKIV FÖR ZOOLOGI. BAND 8. N:0 9. 



vious that this structure enables the larvse to detach a greater 

 portion of the leaf with the mandibles than would be the 

 case if the anterior edge of the labrum were rounded and 

 even. In some Tortr sje-larvse I have even noticed that the 

 edge in the bottom of the incision is serrated, which probably 

 enables the lar va to make use of the labrum to hold the 

 edge of the leaf in the desired position. 



In the leaf-miners we find that the labrum has been 

 modified both as regards its shape, the structures on the 

 ventral and dorsal side. 



30. 



Fig. 28. Labrum of Cemiostoma scitella, ventral aspect. X 496. 

 Fig. 29. » » Nepticula sp., ventral aspect. X 464. 



Fig. 30. » » Omix sp., dorsal aspect. 464. 



The median incision which in Cemiostoma laburnella is 

 very small, becomes in the larva of Cemiostoma scitella deeper, 

 but narrows down to a slit, ending in a rounded hole (fig. 28); 

 the same applies to Lyonetia where the incision is still deeper 

 than in C. scitella, without, however, widening into a hole. 



In many genera, such as Elachista, Nepticula and Tischeria 

 there is no median incision, but the antero-lateral angles pro- 

 ject, and are by two small, rounded incisions set off from a 

 low median lobe, which is sometimes (fig. 29) truncate, so- 



