INTRODUCTION 



different species, and can often be used as a reliable point of 

 distinction between closely-allied species; but they do not 

 seem in general to afford trustworthy characters for wider 

 classification, and are as yet insufficiently studied. Those 

 most readily discernible are two lateral clasping organs, termed 

 the prensors, and a curved upper process, termed the uncus ; 

 these are variously shaped, and often furnished with spines or 

 hooks; they are often accompanied by an expansible tuft of 

 fine hairs, known as the genital tuft, which is a scent-producing 

 organ. 



The legs are made up of coxa, femur, tibia, and tarsus. 

 The coxa, or basal joint, is short and varies little. The femur 

 (plural femora) is sometimes hairy, or furnished with tufts. 

 The anterior tibia is usually comparatively short, and furnished 

 beneath with a median spine-like process, sometimes also with 

 an apical hook ; the middle tibia is normally provided with a 

 terminal pair of spurs, and the posterior tibia with median and 

 terminal pairs of spurs; frequently the posterior tibia (more 

 rarely the middle one) is furnished in the male with an expan- 

 sible pencil of hairs contained in a longitudinal groove, serving 

 as a scent-producing organ ; all the tibiae may be spinose or 

 hairy. Tins tarsus is composed of five joints (the basal being 

 longest), and terminates in two claws; it is often more or less 

 spinose; occasionally it may be partly or wholly aborted, when 

 the leg is modified for other purposes than walking. 



The wings were perhaps originally tracheal gills, respiratory 

 organs afterwards modified for purposes of locomotion. In 

 form they vary from triangular to almost linear, but the 

 triangular shape may be taken as typical. The junction of 

 the wing with the thorax is the base; of the two other angles 

 the upper is the apex, the lower the tomus ; of the three sides 

 the upper is the casta, the lower the dorsum, and the outer 

 the termen. The termen and dorsum arc edged with a fringe 

 of short hairs, the cilia; when, however, the wings arc very 

 narrow, as in many of the Tineina, these cilia are greatly 

 developed in compensation, being sometimes six times as broad 

 as the wing itself. Generally from or near the base of the 

 costa of the hindwing rises a stiff bristle or group of bristly 

 hairs, termed the frenulum, of which the apex passes under a 

 chitinous catch on the lower surface of the forcwing, termed 

 the retinaculum, thus serving to lock the wings together ; the 

 frenulum is commonly single and strong in the male, multiple 

 and weak in the female ; the retinaculum in the female is com- 



