THE MOTHS OF THE BRITISH ISLES. 



Fig. 3. 



Connecting- Bristle 

 and Catch. 



wings eight, but in some genera a rib, or perhaps two, may be 

 absent from the fore or the hind wings ; or an extra rib, some- 

 times two, may be found on the hind wings. These modifi- 

 cations, and others, of the general plan of neuration have been 



employed as a basis upon which 

 to found genera, or to group them 

 together in classification. 



Fig, 3 shows the arrangement 

 by which the upper and lower wings 

 of a moth are united in flight. The 

 bristle {frenulum) arising from the 

 base of the hind wing is held in 

 place by the catch {retinaculum) 

 on the costal nervure of the fore 

 wing. It will be noticed that the bristle of the male is longer 

 and firmer than that of the female. The latter, moreover, is 

 usually made up of two or more strands ; the catch, too, in the 

 female is on the median instead of the costal nervure. These 

 structures are found on the under side of the 

 wings of most moths, but they are absent in all 

 butterflies. The Emperor, Kentish Glory, and 

 Eggars may be mentioned as examples of moths 

 lacking the connecting bristle, but all these 

 have feather-like antennae, which terminate in a 

 point. The Burnets have the antennas gradually 

 thickened towards the tip (A. Fig. 2), and in 

 this respect are somewhat butterfly-like, but these 

 moths have a frenulum. 



The hind wings of the Swifts, and a few others grouped with 

 them, have twelve veins, and these moths have a jugum^ or 

 yoke (see Fig. 4). This is a flap-like projection from the inner 

 margin, near the base, of the fore wing ; it may serve to con- 

 nect the wings when the insect flies, but it does not seem to 

 be capable of giving much help in that way. 



Fig. 4. 



The Jug-um, 

 or Yoke. 



