22 ARKIV FÖR ZOOLOGI. BAND 8. niO 9. 



(fig. 31), in which we still recognize the three lobes known 

 from the tissue-feeders, but where the edge of the lateral 

 lobes are strongly dentate, the teeth increasing in size towards 

 the sides and numbering about 10. 



In Gracilaria (fig. 32) these teeth are fewer (3 — 4) and 

 less developed, and there is no median lobe but a rounded 

 excavation. 



The climax is reached by Lithocolletis (fig. 33) in which 

 the labrum is bilobated, the lobes being shaped as veritable 

 saws, with a dense row of about 10 very sharp teeth dimi- 

 nishing successively in size towards the middle; moreover, 

 the upper surface is radially striated, the strise commencing 

 between the teeth. 



Finally, in Phyllocnistis (fig. 34) the labrum has a shape 

 entirely different from all we have previously seen. 



The two lobes are enormously developed, and project as 

 large tongues behind the base of the labrum; the edges are 

 quite smooth. 



No less astonishing than the shape is the feature that 

 it is on the upper side densely clothed with small, perpen- 

 dicular hairs; the more so as in most of the other genera 

 the primitive 6 pairs of hairs are more or less atrophied. 



Summary. 



Let us now endeavour to find out the function of these 

 different structures of the labrum. In all we have found 

 it modified into four different directions. 



1) Development of the median incision: Cemiostoma, 

 Lyonetia. 



2) Presence of antero-lateral tufts of hairs and hairs and 

 filiform appendages on the ventral side: Elachista, Nepticula, 

 Tischeria. 



3) Saw-shape: Ornix, Gracilaria, Lithocolletis. 



4) Increase in size and presence of numerous perpendi- 

 cular hairs: Phyllocnistis (and to some extent also Ornix). 



1) As to the elongation of the median incision, the fact 

 that in C. scitella it ends with a circular hole seems very 

 suggestive, and, in my opinion, renders the explanation most 

 probable that it is an adaptation which enables the sap of 



