8 ARKIV FÖR ZOOLOGI. BAND (>. N:0 7. 



crements of the lar va, which, contrary to the case with the 

 two other species of the geuns, is liquid. 



If we endeavour to reconstruct mentally, how the blotch 

 is originally formed and låter on expanded, it is obvious 



Fig. 2. Leaf of willow with 9 blotches of O. jiopuli, upper side ; on some 



blotches the upper epidermis is taken away, and they appear quite 



black. Nat. size. 



Fig. 3, 



Leaf of willow, attacked by O. populi; near the top several 

 blotches have coalesced. -/:?. Nat. size. 



that, when the larva emerges from the eggshell and starts 

 eating its way throagh the parenchyma and the results is a 

 blotch-mine, this may be accounted for in two different 

 ways. Either, it turns its head always to one side and thus 

 produces a condensed spiral gallery, where every winding 



