INTRODUCTION. Xlll 



From the middle of the root of each wing two ribs proceed, 

 which usually are united in or behind the middle of the wing, by 

 an interrupted or curved short cross nerve q, thus inclosing a field 

 between it and the root or base. These are called the anterior 

 median nerve, also the subcostal, sc, and the posterior median, or 

 subdorsal, sd. From them and the cross nerve, a number of others 

 proceed which terminate on the anterior and posterior margins. 

 These are counted on the posterior margin from the posterior an- 

 gle toward the anterior angle and are designated by the numbers 

 2, 3, 4, &c. &c., without any regard to the fact whether they arise 

 separately from the median and cross nerves, or whether two or 

 more unite towards the base and proceed from the common branch. 



Besides these, there exist on the interior margin of the wings 

 from one to three nerves (on the primaries usually only one, seldom 

 two), which arise from the base or root, and end on the posterior 

 or interior margin ; these are called dorsal nerves. These aU bear 

 the figure 1, and are distinguished by la, Ib, Ic. On the anterior 

 margin of the primaries and for the most part on that of the se- 

 condaries, a nerve springs from the root, which is called the costal 

 nerve, and which always bears the highest number, as No. 8, fig. 

 22. On the secondaries of many Noctuida, this costal nerve unites 

 with the anterior median for a short distance, fig. 21, or it is en- 

 tirely united with it at the base, so that it seems to proceed from 

 the anterior median itself. The frenulum mentioned above is es- 

 sentially also a nerve, which has remained free from the membrane 

 of the wing. In most butterflies, which have \\ofrenulum, there 

 are in the place of it, on the anterior margin, one or more short 

 curved nerves terminating on it, fig. 22. Nerve 5 of the second- 

 aries is often wanting or is less distinct ; this is also the case with 

 nerve 5 of the primaries ; their position is, however, easily deter- 

 mined by the larger space between 4 and 6, and they as well as 

 other occasionally obsolete nerves are counted, so that each nerve, 

 if possible, may always have the same numerical designation. That 

 nerve at the apex of the primaries on the one terminating nearest 

 to it, is called the apical nerve, fig. 24, 8. 



The two median nerves with their ramifications, and the costal 

 and dorsal nerves, are most prominent in the structure. Each of 

 the medians runs off into three branches, the anterior of the se- 

 condaries into two, so that the individual branches, one after the 

 other, proceed from the principal bough. A more extensive rami- 



