GENERAL 21 



according to the nature of the leaves in which they mine, 

 and with their size, in amount, color, consistency and dis- 

 position. 



A few leaf -miners eject all their frass through a hole in 

 the epidermis of the leaf. The dainty little herb-mining 

 larvae of the genus Cosmopteryx thus keep their mines clean 

 and white. At the opposite extreme are some of the cy- 

 lindric Lepidopterous larvae and the sawflies, whose mines 

 are almost rilled with frass pellets ; also some of the Dipter- 

 ous larvae whose smeared-up mine-walls have a very messy 

 appearance. 



The arrangement of the frass in the mines of certain 

 species is very characteristic. In the mine of the maggot 

 of Phytomyza nigritella on peach and cherry the frass is 

 arranged in a distinct line of spots, that is at once distinctive. 

 So, also is the crossbanded arrangement of it in the winding 

 part of the mine of the trumpet miner of the apple (see figs. 2 

 and 3 of pi. 2). 



The digitate leaf-miner of the locust, Parecopta robiniella 

 maintains a sort of storage cellar for frass down next the 

 lower epidermis of the leaf, while it lives and mines in the 

 palisade layer of cells close to the upper epidermis. It is 

 said to dump its moulted skins, like castor! clothes, into 

 the same receptacle. The makers of linear mines, as they 

 move forward, leave their frass behind in continuous or 

 broken, straight or zig-zag lines or in spots. The polygon 

 miner of the basswood, Lithocolletis luciella, bestows its 

 frass pellets in the extreme periphery of the mine while it 

 feeds from the outside toward the center. Many other 

 mining caterpillars store it in the center, or in one end, often 

 webbing it in place with silk. Most of them keep their 

 feeding areas clear of it. 



TENANCY 



The time during which a leaf mine is occupied may vary 

 from less than a single larval instar to the entire develop- 



