INTRODUCTION. 9 



beinc^ repeated, it progresses by a series of loops and long 

 strides ; heuce, those having this structure are called 

 Gcomctra' (earth-measurers). Those in which fewer pro-legs 

 are absent adopt a modification of both modes of progression, 

 and are commonly called half-loopers. 



]\[ost larva^ have hairs upon their bodies, arising from small 

 raised, hardened disks. Each has sometimes a single delicate 

 bristle or bunch of bristles ; in other cases a spine, simple or 

 branched ; but io many species the covering is much more 

 dense, either short soft down, or hair, short or intermixed 

 with longer, or in part forming thick tufts. The spots or 

 hardened disks are, in many internal-feeding species, and 

 iu those which hide themselves underground, of a shining 

 brown or black, and arranged in a definite pattern on each 

 segment. There is also a plate of a horny or chitinous sub- 

 stance protecting the back of the second segment, and another 

 smaller, upon the thirteenth, above the anal opening. 

 Along both sides above the legs and pro-legs is a complete row 

 of minute orifices called the sjnrades, through which the air 

 is conveyed to a wonderful series of vessels called trachcw, 

 which fulfil the function of lungs. 



Vast numbers of larva? are ornamented with longitudinal 

 lines or stripes, one on the back (dorsal line), one on each 

 side along the spiracles (spiracular line), and another inter- 

 mediate (the suli-dorsal line), or some of these, or additional, 

 and the markings of the larva are usually as reliable and 

 characteristic as those of the perfect insect. Some have, 

 besides, tubercles or processes on various parts of the body, all 

 equally to be depended on for specific identification. 



In treating of species it becomes necessary to adopt some 

 systematic arrangement, and generally species may be readily 

 grouped by structural peculiarities. The characters furnished 

 by the imago state appear to give the most satisfactory re- 

 sults, though these are in some cases supplemented or even 

 modified by those found in the larva, and it appears certain 

 that those characters of the imago iu which both sexes agree 



