GENERAL 7 



to a common form. While all larvae are more or less worm- 

 like, the free-living ones are easily referable to their orders 

 but it is often difficult for a good entomologist to tell whether 

 the creature he has found mining a leaf is the larva of a 

 moth, a beetle, or a sawfly. 



This is true of the more specialized forms only. In each 

 order there are leaf-miners that are not perfectly adapted 

 to the habit, that differ but little from their externally 

 feeding relatives. 



Fig. 4. The four leaf -mining orders and their larva. M, a beetle (Cole- 

 optera) ; JV, a moth (Lepidoptera) ; 0, a fly (Diptera) ; and P, a sawfly 

 (Hymenoptera). 



Speaking broadly it may be said that there are but two 

 kinds of larvae found in leaf mines; the Diptera and the 

 others. 



The Dipterous larvae are very soft and cylindric maggots, 

 very plastic and of no permanent shape, and able to accom- 

 modate themselves to narrow spaces by great changes of 

 form. They readily undergo compression within the shal- 

 low mine. They mostly lie on their sides when mining, and 

 hence this pressure is lateral. Freed from compression 



