December, 1893. ' 278 



over the area (form 2). Here, also, there can be no doubt of the 

 three-fold division, but since the coiling will in some specimens invade 

 for a short distance the last length, and then melt away into the ir- 

 regular arrangement more proper to it, the division is not always so 

 mathematically correct as in lapponica. I should add that this piece 

 of coiling is out and away the best means of distinguishing the mine 

 oifulgens from that of Tityrella, which never has the slightest indica- 

 tion of it in any part of its course — and I must have examined some 

 hundreds of each. 



As regards the apportionment of the mine in the blotch makers, 

 the general rule seems to be that the blotch is begun immediately 

 after the last moult, so that the gallery portion must be allotted to 

 the first three skins, and the blotch to the last. In septemlrella, 

 however, the blotch does not follow quite on the heels of the last 

 moult, and in angulifasciella and arcuatella it is delayed to a still 

 later date. 



One point remains to be considered. It need, perhaps, scarcely 

 be said, that the divisions under which some of these characters have 

 been ranged are to a great extent artificial. The gallery by insensible 

 degrees runs into the blotch ; so, too, there are no sharp boundaries 

 between the various forms of frass arrangement, and they also pass 

 by easy gradations into each other : yet in practice this matters little, 

 provided each species is pretty constant to one mode of working. 

 That by far the greater number are so, even to the smallest particulars, 

 cannot be doubted, but some few indulge in a certain license, and may 

 fairly be called dimorphic, so far as the mine goes ; yet it is a dimor- 

 phism governed, I think, much more by the nature of the leaf than by 

 the mere whim of the insect. Thus, in typical luteella the frass is 

 distributed without any attempt at order, and fills the narrow gallery 

 to about three-fourths of its width, but not unfrequently late in the 

 autumn when the leaves have lost much of their nutritive qualities 

 and the indigestible cellulose has increased, the frass becomes so bulky 

 that it now almost fills the mine, and is at the same time deposited 

 coil fashion, though in a slovenly tentative sort of way, as if the larvae 

 were unused to the practice. Oxyacanthella coils its frass, whether 

 the food-plant be hawthorn, pear or apple. It is noticeable, however, 

 that shortly before its termination the gallery widens somewhat, and 

 concurrently with the change the coiling abruptly stops and the frass 

 is collected into a narrow central thread, showing that the larva is 

 ready enough, when circumstances allow it, to adopt the easier and 

 simpler method of disposal. Now, I have occasionally found, in the 



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