IXTRODUCTION. 3 



iu moths is concealed by the immediate thickening of the 

 body, which appears to join solidly to the thorax. The 

 abdomen contains the digestive and generative organs and a 

 large portion of the complicated breathing apparatus, the 

 remainder of which is in the thorax. 



The wings are attached firmly to each side of the thorax, 

 and consist of a thin double membrane, usually covered on 

 both sides with scales and strengthened by what are generally 

 called nervures or veins, though tendons would be equally 

 appropriate. They cannot be true veins, as they terminate 

 at the ends of the wings, and the name nervures seems most 

 satisfactory, since they certainly carry sensation as well as 

 strengthen the wings. The front of the wing is usually 

 called the costal (or ribbed) margin ; it is the thickest portion, 

 and strengthened by the most powerful uervure, which is 

 often partially doubled. This is known as the suh-costal 

 nervure. From close to its origin in the base of the wing a 

 second nervure proceeds through the middle of the wing, 

 whence it and the sub-costal nervure throw off branches 

 which extend to the margin. Sometimes also these two 

 nervures are united by a cross-bar, which doubtless gives 

 additional strength. The space enclosed is known as the 

 discal cell, and those between the branches of the nervures 

 are also called cells. A third main nervure starts from the 

 base and passes along near to the inner or dorsal margin of 

 the wing — the margin nearest to the ba'k of the insect. It 

 seems to prevent the wing from tearing, and does not throw 

 off branches. The branches from the other two nervures 

 stretch and hold the wing in its proper extended shape, and 

 terminate at fairly equal distances along the hind mav(jin — 

 the portion of the wing farthest from the thorax — or else 

 along the outer half of the front or costal margin. The 

 modifications of these three nervures and their branches are 

 largely made use of in classification. Their general pattern 

 or plan, however, is mainly the same, and the modifications 

 comparatively slight, except that in the extremely narrow- 



