Frenulum of the Lepidoptera. 127 
large number of species have been examined, and in all 
of these the frenulum is found to be entirely wanting. 
The rudiment of the spina may indeed be detected, as is 
observed by Burmeister. It is enclosed in the membrane 
of the hindwing, but is perfectly useless, and does not 
even extend to the edge of the wing. When we consider 
the shape of the wings in this group we perceive that the 
frenulum is not required, as the anterior angle of the hind- 
wing is carried forward in a kind of shoulder almost or 
quite to the costal nervure of the forewing, and as this 
nervure in many species bends back over the surface 
of the wing, it seems probable that during flight the 
prominent shoulder of the hindwing locks beneath it. 
The common silk-worm moth, Bombyx mori, however, 
which has this configuration of wing, still possesses a very 
small rudimentary spina, as do also the two remarkable 
North-American moths, Cicinnus melsheimerti and Lacosoma 
chiridota referred to by Comstock (Study of Insects, p. 357). 
The Uraniidee, so difficult to assign to a satisfactory 
position in classification, exhibit a similar development of 
the humeral portion of the hindwings, and both spina and 
retinaculum are absent so far as the genus Urania is 
concerned. NVyctalemon has in some few instances a very 
imperfect rudiment, but Sematura possesses the appliance, 
although so feebly developed as to be of very little use. 
Coronis, on the other hand, in the thirteen species which 
have come under the writer’s observation, has a frenulum, 
the bristles of which, although rather slender in both 
sexes, are in all cases sufficiently strong to be effective. 
In the Epicopiide the spina is quite rudimentary. 
The late Mr. G. R. Gray in his classification of the 
difficult group Castniide (Trans. Ent. Soc. Lond., i) 
based his division in part upon the development of this 
organ, assigning to some species the possession of three, 
and to others of four, “wing-guides.” Unfortunately the 
specimens, upon which these characters were founded, 
must have been females, as examination shows that this 
singular group is in accord with nearly all others in which 
the frenulum is found, in having the spina single in the 
male and double at least in the female. 
The Notodontidz possess the frenulum, but in many 
species in little more than a rudimentary degree, that of 
Stawropus fagt in particular being very small. 
Amongst the Drepanulide the humeral angle of the 
