128 Mr. G. C. Griffiths on the 
hindwings is largely developed, but all our British Hook- 
tips have a weak and slender frenulum in the male, and a 
small bunch of spinulz in the female, which is probably 
of little or no functional value. The organ is absent 
altogether, according to Hampson and Comstock, in the 
genera Phalacra and Oreta. 
Nearly all the species of the great family Noctuids 
possess the frenulum in normal development, though 
slight variations in the strength of the bristles occur in 
certain genera. Of the genus Stictoptera, however, which 
has not come under the writer’s observation, Hampson 
remarks :—‘ Frenulum of male very strong; single in 
female.” This single spina of the female is very inter- 
esting, as being at variance with all the nearly related 
genera. 
In the Geometride the frenulum is found in the great 
majority of the genera, but, as may be expected from the 
frail and slender structure of their wings and bodies, it 
is of weaker development than in the stronger-bodied 
Noctuide. In the genera Pseudoterpna, Geometra and 
Phorodesma, however, the humeral angle of whose hind- 
wings is much extended, we find in the male the spina 
very weak, and in the female the spinule either nearly 
rudimentary or altogether wanting, whilst in Jodis the 
frenulum is entirely absent in both sexes. In one section 
of Synegia, as defined by Hampson (Moths of India, 11, 
p. 167) the retinaculum is a tuft of hair, in a second it 
forms a large spatulate plate, whilst in a third it is 
described as bar-shaped. Other genera according to the 
same author lack the organ, namely, Genusia, Hypulia, 
part of Naxa, Eucrostes, Paramaxates and Thalera. 
Writing of the Sesiide, Prof. Comstock (Study of 
Insects, p. 260) says :—“ Another remarkable feature of all 
the forms that we have studied is that in the female the 
bristles composing the frenulum are consolidated as in the 
male.” Amongst our British Sesias this holds good in 
respect of Sesia ichnewmoniformis and S. cynipiformis; but 
S. myopxformis 2 and S. tipuliformis 2 (Fig. 15) have 
the spina single for about one-third of its length and bifid 
at the tip. As S. tipuliformis occurs in North America, 
this peculiarity has apparently been overlooked by Com- 
stock ; this is not surprising, as the spina under micro- 
scopic examination appears at first sight to be single, 
and its divided nature is only revealed when subjected 
