134 [Max 



difEculties were not so insurmountable, and were indeed altogether mastered, whcii 

 it struck me that it would be possible, by the insertion of a pin or two, to restore 

 any chamber I had opened to its original form, and so prevail upon ray larva to 

 think that there was not much amiss after all with his house. Armed with this 

 resource, I was able to open the chambers freely, till this part of their history was 

 ascertained. I found that in each chamber the larva moulted once, and that the 

 process was effected very soon, though not quite immediately after the chamber had 

 been made ; the larva, fatigued, as we may suppose, by its exertions, taking a good 

 meal before laying up for the still more exhausting act of moulting. As a conse- 

 quence, the chamber contained frass of two sizes, a small collection of small-sized 

 " frass," and a large collection of large-sized. It then occurred to me that in tlu' 

 "frass " ought to lie the clue for discovering the number of moults that took place 

 in the mine, and I found that by this way of reckoning there must be two, for oi 

 the floor of each mine were collections of two different-sized pellets, in addition to 

 numerous minute particles adherent to the surface of the roof. 



The order of events appears then to be as follows :— The larva on quitting tlu 

 egg, and whilst having the big second segment possessed by so many blotch-mining 

 larvffi, separates the cuticle to the full extent of the mine, leaving its frass, as it goes, 

 upon the membrane ; it then moults, and proceeds to feed upon the parenchyma, 

 having already pi'ctty nearly lost its burrowing form ; it shortly moults a second 

 time, and continues to occupy its quarters until the third moult is close at hand, 

 when it leaves — whether the stock of food be exhausted or not — and makes its first 

 chamber; here the moult is presently accomplished, and the larva remains browsing 

 within till nearly ready for its fourth and final moult ; this point reached, and often 

 with much food still unconsuraed, it goes foraging once more for new quarters, and 

 having met with a leaf suitable for its purpose, it rolls it into the chamber proper 

 to the species, where it contentedly remains till growth is finished. 



So much for their habits. As for the larvte, they are most provokingly alike, 

 and, except in the colour of the head, afford no appreciable specific characters. 

 Sluggish and disinclined to move as they appear to be when their chambers are 

 opened, they really travel pretty quickly wlien in search of fresh quarters. After 

 the loss of the burrowing form, which happens at the first change of skin, the larva 

 is of ordinary shape, neither short nor long, with a large head as wide as the nest 

 segment, and a body of nearly equal width throughout. The skin is semi-transparent, 

 allowing the intestinal contents, and sometimes even tlie tracheal threads, to be seen, 

 and is of a whitish or greenish-white colour, without lines or spots. When full-fed, 

 several of them, including our three species, turu a delicate green. 



I will now take them individually. 



O. popuJetorum. — It usually selects a young leaf for its mine, agreeing in this 

 resiiect with its congeners. Sometimes the mine is on the upper-side, and sometimes 

 upon the under-side. It is on a larger scale than in any of the other species, 

 the gallery being long and rather wide, and tlie blotch large and open ; it is also 

 a more unshapely structure, and is extremely like a Dipterous mine, which also 

 consists cf a gallery and blotch, and is not uncommon in the birch leaves. The 

 larva is careless of the fashion of its first chamber, at one time rolling up half a leaf 

 or a whole one if small, at another simply folding over a piece of the edge, or 

 turning it into a cone ; but of the shape of its final chamber it is most particular. 



