LEAF-MIXERS. 523 



something like the rivers in a map, and which traverse the leaf in 

 various ways. They all, however, agree in one point, namely, 

 their gradual and regular increase in diameter. At their origin 

 they are so small that the finest thread could hardly pass through 

 them, but in proportion as they increase in length they increase 

 in width, so that at their termination they are sometimes the 

 twelfth of an inch in width. 



These marks are the tracks made by very small larvre, which 

 live between the membranes of the leaves, and feed upon the pa- 

 renchyma, or soft substance which lies between the two mem- 

 branes. They follow no rule in their meanderings, but traverse 

 the leaf in a variety of ways. Sometimes they never leave the 

 edge, but follow every little serration of the leaf with perfect ac- 

 curacy. Sometimes they form a kind of spiral, and sometimes 

 they wander irregularly over the whole leaf. Generally, the in- 

 sect does not cross the track which it has once made, being di- 

 verted from doing so by some wonderful instinct. There are in- 

 stances, however, where the insect has crossed its own track, not 

 only once, but several times. 



If the little gallery be opened at the widest extremity, one of 

 three things will be found. Sometimes there is a tiny white grub, 

 very much resembling the larva of certain beetles, and having 

 the rings which represent the thorax rather wider than those 

 which will afterward be developed into the abdomen. As the 

 little creature is able to live between the membranes of a leaf so 

 thin as that of the rose or oak, it is evident, to the most superficial 

 observer, that the insect which will be developed from it must be 

 of very minute dimensions. 



The larva of all winged insects is very large in proportion to 

 the same insects when they have obtained their perfect form, 

 much of the substance being taken up by the wings. As a nat- 

 ural consequence, it follows that the larger the wings, the larger 

 must be the grub, the size of the body being quite a secondary 

 consideration. In the present case, the larvos which we are sup- 

 posed to examine belong to the lepidopterous order, in all of 

 which insects the wings, when present at all, are of great compar- 

 ative size. If, then, the full-grown larva is so small that it can lie 

 concealed between the membranes of a leaf without causing any 

 conspicuous alteration in its outline, it is evident that the perfect 

 insect must be of almost microscopical minuteness. Accordingly, 

 it has been found that the little moths which have been bred from 



