THE NEPTICULIDES. 173 



others short and twisting, and hidden away in a corner of the blotch, 

 as happens in A r . ii-ool/tnjiiflla. Wood writes (Ent. Mo. May., xxix., 

 p. 269) : " It would appear that the gallery was the primitive form, and 

 that the blotch came as an after-development, a view that is strength- 

 ened by other considerations as well. The so-called vermiform mines, 

 which form blotch-like patches on the leaves, are galleries, folded back 

 upon themselves over and over again in a series of coils. They owe 

 their form to the circumstance that the larva confines its operations 

 to the narrow space bounded by two parallel ribs, for as soon as it is 

 brought up by the rib on one side, it turns sharply round until brought 

 up again by the rib on the other side, and so on, backwards and for- 

 wards in this zigzag fashion. Usually strips of tissue are left between 

 the coils, but occasionally the latter inter-communicate freely, and 

 the mine might very well pass for a blotch, were it not that the broad 

 and winding frass- track still remained to indicate its true nature. 

 That some blotches may have originated from these vermiform mines 

 seems likely enough, though probably most of them are merely the 

 natural development of that tendency which some galleries have to 

 widen rapidly and out of all proportion to the growth of the larva, so 

 that it is sometimes hard to decide whether they shall be called 

 galleries or blotches." The mine of N. argentipedalla is in the form 

 of a more or less circular blotch in which no sign of a gallery can be 

 detected. 



The galleries are sub-divided by Wood into (1) wide and (2) narrow, 

 the latter being by far the more numerous. The course of the gallery 

 is of importance, whether straight (usually running by the side of a 

 leaf vein) or curved and twisting, and the same may be said of the 

 commencement of the gallery, for, in this, useful distinctions are also to 

 be found. In some mines, this is straight and fine, in others short and 

 coarse ; some pass directly from the site of the egg, others form little 

 bunches of convolutions, but Wood considers that the arrangement of 

 the frass* in the mine is, if anything, more valuable than any of the 

 other characters for the ready determination of the species. 



In a wide gallery, in which the parenchyma has been well removed, 

 the larva packs its frass behind it in a narrow continuous track down 

 the middle of the mine, whilst in a narrow mine, the larva is obliged to 

 turn its body first in one direction and then in another, in order to find 

 a vacant space in which to deposit the frass, and so the latter is scat- 

 tered irregularly through the mine. In a very narrow or very 

 shallow mine the frass pellets are packed with the greatest precision 

 in slightly curved rows across the mine. From the resemblance of 

 the superimposed rows of pellets when thus arranged, to the coils 

 of a spring, Wood terms this the " coil arrangement." Classifying 

 these then, we get three forms of arrangement : (1) Collected into a 



* With regard to this Wood says: "The various forms of fruss arrangement 

 are of especial interest as illustrating the effect of physical conditions on the habits 

 of an insect, for there can scarcely be a doubt that the various forms that the 

 arrangement of the frass takes, are governed in the main by the transverse capacity 

 of the mine, as this is determined partly by the breadth of the mine, and partly by 

 the extent to which the parenchyma is removed {Ent. Mo. Mag., xxix., p. 270). 



