LEAF MINERS . 
175 
cylinder, they make their way between the two membranes, and 
there remain until they have undergone their transformation. 
The reader must often have seen the leaves of garden plants 
and trees, especially those of the rose, traversed by pale wind- 
ing marks, that look something like the rivers upon a map, and 
having mostly a narrow dark line running exactly along the 
middle. These curious marks are the tracks which are made 
by the various leaf- mining insects, while eating their way 
LEAF MINERS AND ROLLERS. 
through the leaf in which they pass their larval state. In most 
cases, when the insect has completed its term of larval existence, 
one end of the track is found to be greatly widened, and to 
contain either the pupa itself or its empty case. 
The track differs considerably in shape, according to the 
insect which makes it. Sometimes it winds about in the middle 
of the leaf, crossing itself more than once in its progress. 
Sometimes it proceeds in a nearly straight line across the leaf, 
and very frequently, especially in deeply-cut leaves, it follows 
