1890.] 135 



and proceeds by rolling up the leaf longitudinally, using a whole leaf for the pur- 

 pose. Its head, with the excei^tion of the brown mouth parts, is concolorous with 

 the body till the last moult is reached, when it acquires either a very light brown 

 shade, or two pairs of very pale grey streaks down the face. These streaks, of which 

 the outer pair is the larger, are the common form of head-markings in the 

 Gracilaridce. In its mode of spinning up, the larva varies much. Generally, I 

 think, it rolls up a leaf just as it does in making its final chamber, and pupates 

 under the edge of the innermost roll ; not unfrequently it never leaves the feeding 

 chamber at all, but pupates, as in the former case, under the first roll ; whilst, most 

 seldom of all, it spins its cocoon just beneath the edge of a leaf without any rolling 

 up, much as (?./a/coMi/»e«neWa does on alder. The pupa has a faint brown tinge 

 down the back. Its name of popidetorum seems to be a misnomer. Common as it 

 is some years on the birch bushes in the Herefordshire Woods, I have not once seen 

 it on aspen or poplar ; and Mr. Stainton tells me that he hears from Grermany that 

 they breed it there only from birch. 



G. eJongella. — The larva is well known as the roller of the aldei' leaf. Its mine 

 is situated on the upper surface of the leaf, near the margin. The gallery is long 

 and narrow, and twists about until it meets with one of the ribs, down which it 

 turns, the cuticle at the same time being separated for a short distance symmetrically 

 on either side to form the small and narrow blotch ; threads of silk are then spun 

 across the roof from side to side, by the contraction of which the blotch is folded 

 down the middle, and its sides drawn so close together that only a slight sulcus, or, 

 at best, a pale linear mark remains visible on the upper surface ; and as there is 

 little or no distortion of the leaf to catch the eye, it is by no means an easy object 

 to see. Once only have I known the mine to be situated in the middle of the leaf 

 and near the foot-stalk, when the silk threads were powerless to draw the sides of 

 the blotch together, and it had to remain flat and open. The first chamber varies in 

 its shape, but the final one is invariably made by rolling the leaf longitudinally. It 

 never spins up in situ like populetorum, nor does it make any attempt at concealment, 

 but its oval, glistening, and membraneous cocoon is placed quite exposed on the 

 under-side of a leaf and well away from the edge. The back of the pupa varies 

 from a very pale brown to dark grey or smoky-black. In the colour of the larval 

 head the process of development is quite different to what it is in poptiletorum. 

 The head of the very young larva is smoky ; it gets darker with age till it reaches 

 its greatest intensity at the second moult, when it may be described as blackish ; 

 along with the increase of colour is its aggregation into the frontal streaks, the outer 

 pair being for the present continuous with the blackish cheeks and under-parts ; at 

 the third moult the colour goes from the cheeks and under-parts, and only the 

 streaks remain, but of a paler hue than before ; finally, with the fourth moult, the 

 streaks themselves disappear, and the head, except the mouth parts, is left concolorous 

 with the body. This is the typical sequence, but I have noticed in specimens feeding 

 very late in the autumn, long after the great bulk have spun up, or even emerged, 

 that the colour is apt to be very much deeper, and never to be comi^letely lost, so 

 that in the last skin they have heads typical of the penultimate skin of ordinary 

 larvae. 



Such is the life-history of O. elongella on alder, and it is seldom that exceptions 

 in any of the main points occur. Out of some GO or more specimens I have examined, 



