I. TRÄGÅRDH, LEPIDOPTEROUS LEAF-MINERS. 19 



ther back; consequently they are far more exposed to fric- 

 tion and pressure against the walls, and have therefore re- 

 duced the number of joints, in order to diminish in length. 



But the papillae, evidently the most essential part of 

 the antennae, are well developed. 



The difference as to the exposition between the antennae 

 of these genera is also expressed by another feature. 



On the outside of the 2nd joint of the typical larvae (fig. 

 19) we invariably find a long hair, which probably has a 

 tactile function. In the leaf-miners we also find this hair, 

 but it is generally curved evenly curve forward and inwards. 

 This suggests that it is also of protective value to the part 

 of the antenna in front of its point of insertion. 



In the genera Phyllocnistis and Lithocolletis where the 

 above-mentioned neckshaped portion is deeper than in any 

 other and, as a consequence, the antennas better protected 

 than in any other larvae, this hair is very small and incon- 

 spicuous, which seems to justify the assumption that in the 

 other larva its function is to protect the antennae. 



6. Labrum. 



In the previous chapters we have seen how the eyes and 

 antennae have undergone a more or less profound change 

 in the leaf-miners, the ärran gement and number of the former 

 having been altered, the latter reduced etc. 



The labrum has not escaped, but takes also a part in 

 the adaptations, and, as a matter of fact, has in the leaf-miners 

 been modified in several, very interesting directions. 



The labrum is, as a rule, shaped as a transversal plate, 

 with broad base, anteriorly converging, rounded sides and a 

 heart-shaped median incision at the anterior margin which 

 divides it into two rounded lobes. On the dorsal side there 

 are always six pairs of hairs, never more; and on the ventral 

 side 3 pairs of stout bristles. The ventral side is in the 

 posterior */i clothed by the epipharyngeal membrane, which 

 bears numerous, very minute cuticular spines, arranged in 

 transverse rows. 



The median incision is especially developed in those 

 larvae which attack the leaves from the edge ; and it is ob- 



