76 ENTOMOLOGISK TIDSKRIFT IOII. 
and the intersegmental constrictions small; furthermore, the 
body tapers less and more slowly backwards, the prothorax 
has no shields and the head capsule is not, or only to a 
very small extent, covered by the prothorax. 
While, however, in ©. populi the features of the fullgrown 
larva appear already in the 24 instar, in ©. fagz! they do 
not appear until in the 3'd instar, 
The larve differ also in another respect. In the ı° 
instar of O. populi there are no structures for locomotorial 
purposes, whereas in the 1$t instar of O. fag? there are on the 
abdominal segments I—VII a pair of comparatively large 
locomotorial bristles, laterally. 
During the further growth of both larvæ structures for loco- 
motorial purposes develop, especially dorsally and ven- 
trally, in ©. populi also laterally, the cuticular granule being 
pointed on the lateral projections, semispherical on the rest 
of the body — in ©. fagi preferably dorsally, where the 
thin transversal, naked areas at the top of the abdominal 
segments I—VII presumably are of locomotorial use. 
Thus, in ©. fagz the ı°t instar, and to a certain extent 
also the 24 one, as the lateral bristles exist beside the cu- 
ticular spinulæ, are provided with lateral locomotorial struc- 
tures, while in the subsequent instars they are provided espe- 
cially with dorsal ones. 
Formation of the mines. 
This difference suggests that during these stages of its 
development the conditions under which the larva lives its life 
as a miner are different. And this is also the case. During 
the earlier period of its life the larva is exclusively a tunnel- 
miner, later it becomes a blotch miner. 
From the egg-chamber in the median nervule the larva 
makes a narrow gallery, running more or less parallel to a 
side nervule, straight, or only slightly winding, towards the 
! It ought to be pointed out, that I have not been able to follow 
one larva of either species during its development, but have applied the 
terms »1ISt instar etc.» according to the different sizes of the larvæ com- 
bined with the structural differences. 
