52 LEAF-MINING INSECTS 



Microlepidoptera and especially among the leaf-miners very 

 many intermediate forms. In these, the prolegs may be 

 indicated only by the presence of crochets with all indica- 

 tion of a swelling lacking or the reverse. 



In some families (Tischeriidae, Gracilariidae), these cro- 

 chets may be found representing the prolegs while thoracic 

 legs may be entirely wanting. In the former family thoracic 

 legs are never present and the crochets are found on seg- 

 ments 3, 4, 5 and 6 of the abdomen. In the Gracilariidae, 

 however, thoracic legs are present in the Gracilarinae, 

 present or absent in the Lithocolletinae, but the prolegs 

 represented by crochets or modified into suckers, appear 

 only on segments 3, 4 and 5 of the abdomen, a feature not 

 found save in this family. 



Nepticula has neither segmented thoracic legs nor cro- 

 chets, but there are present fleshy leg-like swellings on 

 segments 2 and 3 of the thorax and segments 2, 3, 4, 5, 6 

 and 10 of the abdomen. 



In some cases the prolegs are reduced though the thoracic 

 legs be well developed. Thus, in the genus of case-bearers, 

 Coleophora, which, after their leaf-mining infancy is past, 

 will walk around on their thoracic legs bearing their abdo- 

 men and its enveloping case aloft behind, the thoracic legs 

 have need to be stout but the prolegs are in all stages of 

 reduction until in Coleophora limospinnella the crochets are 

 lacking entirely. In the case-bearers there is also the tend- 

 ency for the two rows of prolegs to approach one another on 

 the mid-ventral line so that the crochets which are all of 

 one size and in one row will form nearly continuous trans- 

 verse bands. In some of the mining Gelechiidae also the 

 prolegs are much reduced. 



In Bucculatrix the prolegs are long and slender, but this 

 accords with the fact that Bucculatrix is a miner for but a 

 short time, and the long prolegs become useful in the course 

 of external feeding. 



