I. TRÄGÅRDH, LEPIDOPTEROTTS LEAF-MINERS. 



39 



It is difficult to teli which of these two processes was 

 the primary one, bnt there is reason to believe that the 

 formation of a thin, flat and comparatively large lower lip 

 is a very essential feature in the mouth-parts of the miners, 

 to judge from the different ways in which it has been 

 achieved. And as in Nepticula and Elachista the spinneret 

 has been adapted to that purpose, we may fairly conclude 

 that in the other genera here discussed the reduction and 

 retrogression of the spinneret had already been at least partly 

 achieved, when the necessity for a thin and flat lower lip 



arose. 



In Nepticida and Elachista, on the other hand, we may 

 reasonably presume that they descend from larvse, the spin- 

 neret and labial palpi of which were of the shape typical in 

 the external leaf-feeders, or which were perhaps (comp. p. 37) 

 more primitive. Consequently, the spinneret became modified 

 in the direction desirable, which saved it from destruction. 

 The larva of Tischeria, on the other hand, still preserved 

 the use of its spinning apparatus, but it became hidden for 

 the greater part underneath a thin horizontal fold of the 

 mentum, whose function may possibly be to form a smooth 

 surface, enabling the larval head to be pushed forward when 

 the mine is being enlarged. It is at least conceivable that such 

 a comparatively large structure would othervise be a hindrance 

 during this procedure. In Tischeria there is also a thin lower 

 lip, which is even larger than in the other genera, and 

 moreover projects further forward than in these. In Ti- 

 scheria the problem is solved in quite a different way, the 

 palpiger being highly developed and forming a pair of large 

 ovoid, thin blades, which all but meet in the median line, 

 where the top of the hypopharynx projects. 



Concerning the shape of the spinneret in Nepticula, we 

 must not loose out of sight the possibility that the flat type 

 may be the most primitive one. Nepticula is in several 

 respects a very primitive genus [comp. Trägårdh 16 p. 1] and 

 in this particular respect it agrees with the larva of Lima- 

 codes testudo in which Chapman [11, p. 347] describes it in the 

 following way. »The spinneret in this larva is remarkable 

 up till the penultimate stage, in being not a pointcd organ, 

 but flattened out like a fish's tail, and the silk it disposes 



