10 



INTKOBUCTION. 



costa or vein 1 and inner margin may be present. The present 

 form of neuration arose from a system of simple longitudinal veins, 

 which by the union of their basal portions formed the present 

 branching system ; thus the discocellulars which close the cell of 

 each wing were formed by the junction of the basal portions of the 

 three radial veins, the basal stem being then aborted, leaving only 

 an outwardly-directed trifid fork of which the radials are the 

 extremities. The whole process in its various stages may be clearly 

 seen in such generalized forms as the Cossidce, Psychidce, and 

 Zygcenidce ; and the neuration of the extinct ancestor of the Lepido- 

 ptera must have consisted of at least fifteen simple longitudinal 

 veins in each wing, and probably more, as in several groups vein 1 h 

 of the hind wing is forked at base. Vein 4, the lowest radial, has 

 become permanently connected with the two-branched median 

 nervure *, and vein 6, almost without exception, with the five- 

 branched subcostal nervure ; but the position of vein 5 diifers much 

 in the several groups of families, according to whether it retains its 

 original medial position or is attracted towards the median or 

 subcostal systems. 



The fore and hind wings in the majority of families of Moths 

 are connected by the " frenulum " developed from hairs arising from 

 the base of the costa of hind wing and fitting into the " retinaculum " 



— mil. 



Fig. 6.— 1. S ■ -• 2 • (From Moths of India, vol. i.) 

 A. Fore wing. B. Hind wing. 

 /. Frenulum. s.n. Subcostal nervure. 



r. Retinaculum. 

 c.ii. Costal nervure. 



m.n. Median nervure. 

 i 71. Internal nervure. 



on the fore wing, which consists of a fold from the underside of the 

 costa, a membranous hook, or tuft of hair arising from the costal 

 nervure, or a tuft of hair arising from the median nervure or rarely 

 from the wing-membrane below it. The form of the frenulum is 

 of great use in determining sex, as in the males of all the forms 

 that possess it, it consists of hairs firmly soldered together so as to 

 form a single bristle, articulating with the retinaculum arising from 

 the costal nervure, whilst in the female it consists of three or more 

 bristles (in a Cossid I have fouud as many as nine) articulating 

 with the retinaculum arising from the median nervure. In the 



* A. Spuler, ' Zur Phylogenie und Ontogenie des Fliigelgejiders der Schmet- 

 terlinge.' 



