WING-NERVULES 



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 re- 

 member 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, 1), 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 num- 

 bers 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, 11-1-1 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 ligjiiperda). In 

 Hepialus and Ilicropteryx (the jugate moths of Comstock) the 

 hind wings are less dissimilar in nervuration from the front 

 wings than they are in other Lepidoptera.^ 



Internal Anatomy." — The alimentary canal extends as a long, 



1 The structure and development of scales and nervures is dealt with as part of 

 the brief study of the development of the wing, on p. 329, etc. 



2 The internal anatomy of Lepidoptera has not been extensively studied. For 

 information refer to Dufour, G.R. Ac. Paris, xx.xiv. 1852, p. 748 ; Scudder, Butt. 

 New England, i. 1889, p. 47 ; Minot and Burgess, Fourth Hep. U. S. Entom. Comm. 

 1885, p. 53. 



Fig. 162. — Wing - nervuration of 

 Castnia. Undersides of, A, front, 

 B, hind wings, la, 16, Ic, Id, 

 Inner marginal nervures ; 2, lower 

 branch of median ; 8, subcostal 

 of hind wing ; 12, subcostal of 

 front wing ; e, " stalk " of 8 and 

 9 ; /, frenulum ; r, retinaculum ; 

 s, shoulder ; g, articulation of 

 wing. 



