xii INTRODUCTION. 



is called the apex, and the angle between the termen and the dorsum the tonviK (see 

 Plate I., fig. 1). The termen and dorsum are edged with a fringe of hair-like scales, termed 

 the cilia. At the base of the hind-wings is generally situated a stiff bristle, or several stiff 

 hairs, called the frenulnm, the ends of which pass through a chitinous process on the 

 under side of the fore-wing near the dorsum. This process is termed the retinaculum, and 

 serves, in conjunction with the frenulum, to lock the wings together during flight. In 

 the female both these organs are often very imperfectly developed, the frenulum consisting 

 of several bristly hairs, and the retinaculum of a group of stiff scales. In many of the 

 Lepidoptera both frenulum and retinaculum are entirely wanting. 



"In the Micropterygina, a membranous or spine-like process called the jugnm rises 

 from the dorsum of the fore-wing near the base and passes under the hind-wing, which is 

 thus held between the process and the overlapping portion of the fore-wing." (Meyrick.) 



The veins of the wings are thus described by Mr. Meyrick : 



"The wings are traversed by a system of Veins tubular structures which serve at 

 once as extensions of the tracheal system, and to form a stiff framework for the support of 

 the wing. In the normal type of Lepidoptera the fore-wings possess three free veins 

 towards the dorsum, termed la, 16, and Ic ; a central cell, out of which rise ten veins, 

 numbered 2 to 11, the sides of the cell being known as the upper median, lower median, 

 and transverse veins respectively ; and a free subcostal vein, numbered 12 ; whilst the 

 hind-wings differ from the fore-wings in having only six veins rising from the central cell, 

 numbered 2 to 7, so that the free subcostal vein is numbered 8 (see Plate I., figs. 3 and 4, 

 assumed type of neuration of a Lepidopterous insect). In some forms a forked parting- 

 vein traverses the middle of the cell longitudinally, and a second parting-vein traverses the 

 upper portion, so as to form a secondary cell ; but these are more frequently absent or 

 represented only by folds in the membrane. In a few forms there is a tendency to the 

 production of several false veins, termed pseudonenria, appearing as short branches from 

 the subcostal vein of the hind- wings to the costa ; these are thickenings of the membrane, 

 and are commonly very irregular and variable, often uneven in thickness or incomplete. 

 Sometimes one of these near the base is better developed and more permanent in 

 character; it is then termed the prtecostal spur (see Plate I., figs. 8 9 and 27 9 ). Modi- 

 fications in the general arrangement of the veins may arise through any of the following 

 processes, viz. : (1) obsolescence, when a vein loses its normal tubular structure, becoming 

 attenuated and reduced in substance, until it appears a mere fold of the membrane (Plate 

 II., fig. 60, vein 5 in hind-wings of Selidosema) ; (2) stalking, when the two veins are fused 

 together for a portion of their length from their base, so as to appear to rise on a common 

 stalk (Plate II., fig. 34, veins 6 and 7 in hind-wing of Hydriomena) ; (3) coincidence, when 

 two veins are fused together for the whole of their length, so that one appears entirely 

 absent, an extreme form of stalking ; (4) anastomosis, when two veins rise separate, meet, 

 and are fused together for a certain distance, and then separate again (Plate II., fig. 23, 

 veins 7 and 8 in the hind-wings of the ? of Tatosoma) ; (5) concurrence, when a vein 

 rises separate, runs into another, and does not separate again, an extreme form of 

 anastomosis ; (6) connection, when two veins are connected by a short transverse bar 

 passing from one to the other, a special form of anastomosis, evolved from the ordinary 

 form under the influence of a tendency to lateral extension (Plate II., fig. 28, veins 

 7 and 8 in hind- wing of Paradetis}. Vein U in both wings is often furcate at the base. 



