XVI INTRODUCTION. 



are called sagittate spots. Besides these, the Noctuidce or moths, 

 have three distinguishing marks in the middle area; one in the 

 cell, lb, called the dentiform spot; a small, usually round one in 

 the median cell, called the orbicular, mo, and behind it, a larger, 

 kidney-shaped spot, called the reniform, mr. The two latter are 

 often surrounded by a double edge, lighter than the ground color. 

 Between both, there is usually drawn across the whole wing, a darker 

 band, which is called the transverse median shade, am. Some spe- 

 cies have a dark square spot between the two spots in the median 

 cell, which often extends itself in a pyramidal form over the orhi- 

 cidar towards the root, so that both spots form a sort of recumbent 

 pyramid, and is called the pyramidal spot. The posterior trans- 

 verse streak alone is for the most part continued over the second- 

 aries, which is then called, on both sides of the wing, the arcuated 

 line. 



The reniform mark appears on the under side as the median 

 lunule, and all the dark spots on the cross nerve of both sides of 

 the secondaries bear the same name, fig. 21. 



In general, the structure of the several parts of the butterfly, as 

 far as this is necessary to the determination of the species, genus, 

 etc. , can easily be recognized, without dissection. DifBculties some- 

 times occur in the frequently indistinct simple eyes, pcdpuli and 

 frenulum. The last is usually present in species which fold their 

 wings, when in a state of rest. A careful examination with a 

 magnifying glass will readily detect the presence of this member. 

 Much more difficult is a discrimination of the nerve structure, inas- 

 much as the nerves are frequently so covered with scales, that with- 

 out removing them, the nerves cannot be seen. In this case, the 

 under side of the wings should be particularly examined, inasmuch 

 as the nerves on this side are more distinct than on the other. But 

 if this will not suffice to determine all the points desirable to be 

 known, the scales must be removed. In order to accomplish this, 

 either take a sharp, fine penknife and move the blade or back gen- 

 tly over the nerves on the under side of the wings, until the nerves 

 become distinct, or rub the whole wing with a soft, blunt hair pen- 

 cil until all the scales are removed, but on the upper side only, 

 when you wish to observe the furcation of the dorsal nerves of the 

 primaries. This operation can be most satisfactorily performed 

 when the specimens are fresh. 



