50 LEAF-MINING INSECTS 



of the insect to place them where she does. For example, one 

 species will lay on the upper side, and another, for no apparent 

 cause, on the under side of the same leaf, and yet each will cling 

 to its own habit as it were a matter of vital importance. 



In hatching the larvae of some miners come through the 

 egg shell on its exposed surface and afterwards burrow into 

 the leaf, but a larger proportion burrow through the egg 

 shell and into the leaf in one operation. Some larvae, 

 especially those of the family Gracilariidae, are able to eat 

 only in the plane of the long axis of their bodies; and it is 

 only by virtue of their purchase on the egg shell and by 

 taking a diagonal path into the leaf that they are able to 

 effect an entrance. Nepticula has not the limitation of 

 early "Gracilarian" head-parts, but the head has so come 

 into alignment with the body and is so sunk into the pro- 

 thorax that it w r ould be equally helpless to enter a leaf from 

 its surface. The Coleophorae, case-bearers, seem quite 

 capable of eating at right angles to their bodies: and of 

 those that are miners, some, as Coleophora laricella, bore 

 from the egg directly into the leaf while others, as Col- 

 eophora fletcherella are naked exposed larvae for several 

 hours. There is probably advantage in leaving no open 

 door in the dwelling for the admission of such unwelcome 

 guests as fungi and bacteria. 



The larva. The larvae as they issue from the eggs are very 

 minute. The number of times it is necessary for them to 

 shed their skins to allow for new growth varies with genus 

 and species and possibly at times even with the individual. 

 Lithocolletis "of the flat group" (the Cameraria group) 

 is said to moult seven times, w T hile Nepticula moults three 

 or four times. These probably represent the extremes of 

 variation in this order, in which five is the usual and ordi- 

 nary number of moults. 



The form of the various leaf -mining larvae departs more 

 or less widely from that of free-living caterpillars. Judged 



