Turning to the mode of designation of the nervures,[177] we may commence by remarking that no system satisfactory from a practical as well as from a theoretical point of view has yet been devised. The diagrams given in figure 161 will enable us to explain the methods actually in vogue; I. representing the system, dating from the time of Herrich-Schaeffer, chiefly used by British naturalists, and II. that adopted by Staudinger and Schatz in their recent great work on the Butterflies of the world. The three anterior nervures in both front and hind wings correspond fairly well, and are called, looking at them where they commence at the base of the wing, "costal," "subcostal," and "median" nervures. The nervures near the inner margin of the wing (that is the lower part in our figures) differ much in the front and hind wings, consisting either of two or of three separate portions not joined even at the base. British entomologists call these "branches or divisions of the internal nervure": the Germans call the more anterior of them the "submedian," and the more internal the "inner-margin nervure"; they are also frequently called anal nervures. The cross-nervure that closes the cell is called discocellular; when apparently composed of two or three {319}parts joined so as to form angles, the parts are called, according to position, upper, lower, and middle discocellulars. One or more short spurs may exist on the front part of the basal portion of the hind wing; these are called praecostal. The branches or terminal divisions of the nervures should be called nervules; they are usually mentioned by the numbers shewn in the diagram (Fig. 161, I.). In addition to this, it is only necessary to remember that number 2 is always assigned to the posterior division of the median nervure, the nervules below this being all called 1, and distinguished by the addition of _a_, _b_, _c_ when requisite. This course is necessary, because if it were not adopted the corresponding nervules on the front and hind wings would bear different numbers. The use of this system of numbers for the nervules is becoming general, and it answers fairly well for practical purposes. On the other hand, extreme discrepancy exists as to the nomenclature of the nervures and nervules, and there are almost as many systems as there are authorities. The normal number of nervules is, on the front wing, 11 + 1 or 2 inner marginal, and on the hind wing 7 + 2 or 3 inner marginal. In the aberrant moths of the genus _Castnia_ the nervuration is unusually complex and irregular (Fig. 162), and an analogous condition occurs in our common Goat-moth (_Cossus ligniperda_). In _Hepialus_ and _Micropteryx_ (the jugate moths of Comstock) the hind wings are less dissimilar in nervuration from the front wings than they are in other Lepidoptera.[178]