INTRODUCTION 



monly represented by a group of stiff scales. When there is 

 no frennhim, the costal area of the hindwing is generally 

 dilated basally, so as to rest more firmly against the forewing, 

 and avoid dislocation. But in the Micro'pterygina (as recently 

 discovered by Professor Comstock) a different' system prevails ; 

 a membranous or spine -like process called the jugum rises 

 from the dorsum of tiie forewing near the base, and passes 

 underneath the hindwing, which is thus held between the 

 process and tlie overlapping portion of the forewing. 



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 forewings possess 

 three free veins towards the dor- 

 sum, termed la, lb, 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 i-espectively ; and 

 a free subcostal vein, numbered 

 12 : whilst the hindwings differ 

 from the forewings in having only 

 six veins rising from the central 

 cell, numbered 2 to 7, so that the 

 free subcostal vein is numbered 8. 

 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 pi'oduction of several 

 false veins, termed pseudoneuria, appearing as short bi'anches 

 from the subcostal vein of the hindwings to the costa ; these are 

 thickenings of the membrane, and are commonly very irregular 

 and variable, often uneven in thickness or incomplete. Some- 

 times one of these near the base is better developed and more 

 permanent in character ; it is then termed the praecostal spur. 

 Modifications 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 



Assumed type of nenration of 

 tlie Lepidoptera. 



