ORDER LEPIDOPTERA 51 



by numerical abundance, success in leaf-mining seems to be 

 directly proportional to the extent of modification. Prob- 

 ably modification has been by losses of parts more often 

 than by accessions. Spines, for instance, would be almost 

 prohibitive and are not to be found, even the setae being 

 exceedingly small. The body has become flattened, es- 

 pecially in early instars of the sap feeders. As though to 

 compensate for the decrease in height, the segments in many 

 cases have become bulged out at the sides. From above, 

 each larvae have something of the appearance of a chain of 

 beads. 



Well developed legs are not much needed where there is 

 little distance to go and scant room to go in. Hence we find 

 the legs in all stages of reduction from fairly well developed 

 to entirely wanting. Eriocrania have larvae that are en- 

 tirely footless throughout larval life ; so, also have Heliozela 

 and Antispila. Phyllocnistis has no legs corresponding 

 either to the thoracic legs or to the prolegs of other cater- 

 pillars, but slanting downward from the sides of each 

 abdominal segment except the last are membranous out- 

 pushings of the body wall, homologous, not with prolegs, but 

 with the mamillations at the sides of the segments of other 

 mining larvae. 



In free-living caterpillars ordinarily there are three pairs 

 of horny segmented thoracic legs and five pairs of fleshy 

 abdominal legs; i.e., prolegs on abdominal segments 3, 4, 5, 6 

 and 10. The prolegs are usually provided with a band or 

 circlet of hooks or "crochets" whose arrangement and form 

 differs sufficiently to make them a useful character in classi- 

 fication. Chapman was the first to call attention to the 

 fact that the crochets of "Micros" are usually arranged in a 

 simple or multiserial circle while those of the "Macros" 

 are usually placed in a longitudinal row. 



Between the footless condition mentioned above and the 

 typical sixteen-legged caterpillars there are among the 



